i 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


GIFT  OF 

Arthur  1,1,   Johnson 


Map  showing  the  soil  provinces  and  soil  regions  of  the  United  Stat 


Bureau  of  Soils,  Bui.  Ofl.  1013.    (CYmrtpsy  The  Macmillan  Company.) 


T.ippiNCOTT's  COLLEGE  TEXTS 

AGRICULTURE 

EDITED  BY  K.  C.  DAVIS,  PH.D.  (CORNELL) 

SOIL  PHYSICS  AND 
MANAGEMENT 


BY 


J.  G.  MOSIER,  B.S. 


PROFESSOR  OF  SOIL  PHYSICS,  UNIVERSITY  OF  ILLINOIS;     CHIEF  OF  SOIL    PHYSICS, 
AGRICULTURAL   EXPERIMENT   STATION 

AND 

A.  F.  GUSTAFSON,  M.S. 

ASSISTANT   PROFKSSOR    OF  SOIL   PHYSICS,    UNIVERSITY   OF   ILLINOIS;      ASSISTANT 
CHIEF   OK   SOIL  PHYSICS,  AGRICULTURAL   EXPERIMENT  STATION 


202  ILLUSTRATIONS  IN  THE  TEXT 


PHILADELPHIA  &  LONDON 
J.  B.  LIPPINCOTT  COMPANY 


COPYRIGHT,    1917.   BY   J.   B.    LIPP1NCOTT   COMPANY 


Electrotyped  and  Printed  by  J.  B.  Lippincott  Company 
The  Washington  Square  Press,  Philadelphia,  U.S.  A. 


PREFACE 

THIS  book  is  written  for  three  purposes:  first,  as  a  text-book 
0^  for  agricultural  students ;  second,  as  a  reference  book  for  the  prac- 
^  tical  farmer;  and,  third,  as  an  aid  to  the  land  owner  who  desires 
ij  information  in  the  personal  management  of  his  land. 

Soil  physics  is  the  application  of  physics  to  soils.  It  is  so 
^  closely  related  to  other  sciences  that  it  becomes  necessary  to  trespass 
upon  the  ground  of  some  of  them,  notably  botany,  geology,  chem- 
istry, and  zoology,  to  present  certain  subjects  clearly  and  com- 
pletely. Soil  physics  dovetails  in  with  the  closely-related  phases 
of  agronomy,  as  soil  biology,  soil  fertility,  crop  production,  and 
agricultural  engineering,  to  such  an  extent  that  it  is  necessary  to 
give  material  very  closely  related  to  all  of  these. 

An  attempt  has  been  made  to  emphasize  the  principles  of  soil 
hysics,  omitting  the  details  of  practice  except  where  necessary  for 
purposes  of  illustration.    Although  the  book  is  written  in  the  Middle 
West,  yet  the  principles  given  apply  anywhere. 
«         The  arrangement  of  the  matter  presented  has  been  carefully 
\$  planned  from  the  teaching  standpoint,  and  has  been  tested  in  the 
VL     classroom  for  several  years. 

^*^     Various  sources  of  information  have  been  used  by  tlie  authors 
and  acknowledgment  made  accordingly. 

,T.  (i.  MOSIKH, 

A.     F.     (lUSTAFSOX. 
College  of  Agriculture, 
University  of  Illinois, 
Urbana,  111.,  October,  1!)17. 


CONTENTS 


CHAPTER  PAGE 

I.  SOIL  MATERIAL  AND  ITS  ORIGIN 1 

Definition  of  Soil — Elements  of  the  Earth's  Crust— Soil 
Forming  Minerals — Rocks — Igneous  Rocks — Aqueous 
Rocks — Metamorphic  Rocks. 

II.  WEATHERING 11 

Physical  Agencies — Heat  and  Cold — Freezing  and  Thaw- 
ing— Glaciers — Erosion  of  Streams — Waves — Wind — 
Plants — Chemical  Agencies — Acids — Carbon  Dioxide — 
Oxidat  ion — Deoxidation — Hydration — Solution — Plants 
— Animals. 

III.  THE   PLACING  OF  SOIL   MATERIAL.     I.  RESIDUAL,  GRAVITY- 

LAID  AND  WATER-LAID  DEPOSITS 27 

Sedentary  Formations — Residual  Soils — Cumulose  Soils — 
Swamps  and  Marshes — Transported  Formations — Col- 
luvial  or  Gravity-laid  Soils — Sedimental  or  Water-laid 
Soils. 

IV.  THE  PLACING  OF  SOIL  MATERIAL.     II.  GLACIAL  OR  ICE-LAID 

DEPOSITS 41 

The  Glacial  Period — The  Jerseyan  or  Nebraskan  Glacia- 
tion — The  Kansan  Glaciation — The  Illinoisan  Glaciation 
— The'Iowan  Glaciation — The  Early  Wisconsin  Glaciation 
— The  Late  Wisconsin  Glaciation — Incidental  Features. 

V.  THE  PLACING  OF  SOIL  MATERIAL.      III.  EOLIAL  OR  WIND- 
LAID  DEPOSITS •. 53 

Classes  of  Wind-laid  Material — Dunes — Loess — Adobe — 
Volcanic  Dust. 

VI.  SOIL  AND  SUBSOIL 67 

The  Top  Soil— Surface— Subsurface — Subsoil— Tight  Clay 
— Hard  Pan — Humid  and  Arid  Subsoils — Plow  Sole. 

VII.  CLASSIFICATION  OF  SOILS 72 

Need  of  Classification — Basis  of  Classification — Geological 
— Lithnlngicnl  —  Tem|>eraturc- —  Moisture  — •  Arid  Soils  — 
Humid  Soils — Vegetation — Color — Texture. 

VIII.  CLASSIFICATION  nv  THE  BUREAU  OF  Soius 78 

Soil  Province — Soil  Region — Soil  C'lass — -Soil  Type — Pied- 
mont Plateau  Province — Appalachian  Mountain  and  Pla- 
teau Province — -Limestone  Valleys  and  Uplands  Province — 
Glacial  and  Ix>essial  Province — Glacial  Lake  and  River 
Terrace  Province — Atlantic  and  Gulf  Coastal  Plains 
Province — River  Flood  Plains  Province — Great  Plains 
Region — Rocky  Mountain  and  Plateau  Region — North- 
western Intermountain  Region — Great  Basin  Region — 
Arid  Southwest  Region — Pacific  Coast  Region. 


CONTENTS 

IX.  SUB-PROVINCES,  CLASSES,  TYPES,  AND  SURVEYS 112 

Sub-provinces — Soil  Classes — Soil  Types — Naming  of  Soil 
Types — Classes,  Types,  and  Phases  in  Illinois — Soil 
Surveys — Surveys  in  Different  States — Objects  of  a  Soil 
Survey — Methods  of  the  Survey — Sampling  of  Soils. 

X.  MINERAL  CONSTITUENTS 123 

Soil  Particles  and  Their  Separation — Mechanical  or  Physi- 
cal Analysis — Methods  of — Mineral  Soil  Constituents  and 
Their  Properties — Colloids — Colloids  in  Soils — Mineral 
Colloids — Clays  and  Clay  Loams — Silt  and  Silt  Loams — 
Sands  and  Sandy  Loams — Gravel  and  Gravelly  Loams — 
Stones. 

XI.  ORGANIC  CONSTITUENTS  OF  SOILS 142 

Kinds  of  Organic  Matter — Amount  of  Organic  Matter  in 
Soils — Changes  of  Organic  Matter — Nitrogen  Content  of 
Humus — Distribution  of  Organic  Matter  in  the  Soil  Strata 
— Value  of  Organic  Matter  to  Soils — Losses  of  Organic 
Matter — Estimation  of  Organic  Matter. 

XII.  MAINTAINING     AND     INCREASING      THE     ORGANIC-MATTER 

CONTENT  OF  SOILS 158 

Addition  of  Limestone — Application  of  Phosphorus — 
Accumulations  in  Pastures—Green  Manures — Catch  and 
Cover  Crops — Barnyard  Manures — Loss  of  Manure  and 
Its  Prevention — Methods  of  Applying  Manure — Organic 
Residues — Growing  Non-tilled  Crops — Rotatio  nof  Crops. 

XIII.  PHYSICAL  PROPERTIES  OF  SOILS 175 

Real  or  Absolute  Specific  Gravity — Apparent  Specific 
Gravity — Weight  of  the  Soil — Color  of  Soils — Odor  of  Soils 
— Number  of  Particles — Shape  of  Particles — Arrangement 
of  Particles — Internal  Area  of  Surface — Porosity  of  Soils. 

XIV.  WATER  OF  SOILS 186 

Some  Physical  Characteristics  of  Water — Specific  Heat — 
Viscosity — Uses  of  Water — Amount  of  Water  Required 
by  Plants — Dependent  Upon  Transpiration— Supply  of 
Moisture  in  Soils — Ways  of  Expressing  Moisture  Content. 

XV.  WATER  OF  SOILS.     I.  HYGROSCOPIC  MOISTURE 194 

Determination  of  Hygroscopic  Coefficient  of  Soils — Use  of 
Hygroscopic  Moisture. 

XVI.  WATER  OF  SOILS.    II.  CAPILLARY  WATER 199 

Surface  Tension — Moisture  in  Soil  Columns — Effect  of 
Size  of  Soil  Particles — Moisture  Equivalent — Determina- 
tion of  Moisture  Equivalents  from  Other  Soil  Constants — 
Movement — Thickness  of  the  Film — Viscosity — Texture — 
Organic  Matter — Maximum  Capillary  Capacity  or  Moist- 
ure-holding Capacity  of  Soils — Amount  of  Water  Moved 
by  Capillarity — The  Capillary  Pull  of  Soils — Osmosis  in 
Soils — Use  of  Capillary  Water — Wilting  Coefficient — 
Available  Moisture. 

XVII.  WATER  OF  SOILS.    III.  GRAVITATIONAL  WATER 217 

Percolation — Physical  Composition  or  Texture — Granula- 
tion—Organic Matter — Viscosity — Atmospheric  Pressure 
—Shrinkage  Cracks — Roots  of  Plants — Lysimeters  or 
Drain  Gages. 


CONTENTS  vii 

XVIII.  CONTROL  OF  MOISTURE.    I.  DRAINAGE 222 

Removal  of  Excess  of  Water — Stability — Granulation — 
Available  Moisture — Aeration — Temperature — Decompo- 
sition and  Nitrification — Heaving — Erosion — Types  of 
Drainage — Open  Drains — Tile  Drains. 

XIX.  CONTROL  OF  MOISTURE.    II.  TILLAGE 230 

Moisture  Capacity  of  Soils — Excess  of  Moisture — Losses 
from  Soils — Artificial  and  Soil  Mulches — Fineness  of 
Mulch — Depth  of  Mulch — Maintenance  of  Mulch. 

XX.  CONTROL  OF  MOISTURE.     III.  DRY-LAND  AGRICULTURE 238 

Adaptation  of  a  Region  to  Dry  Farming — -Water  Require- 
ments of  Plants — Loss  of  Water — Method  of  Preventing 
Loss  of  Water — Tillage — System  of  Cropping — Crops  for 
Dry  Farming — Seeding — Acclimated  Seed. 

XXI.  CONTROL  OF  MOISTURE.     IV.  IRRIGATION 257 

Area  and  Projects — Sources  of  Water — Preparation  of 
Land  for  Irrigation — Character  of  Water  Used  for  Irriga- 
tion— -Composition  of  River  Sediments — Time  of  Irrigation 
— Amount  of  Water  to  Apply — Loss  of  Water  from  Canals 
— Duty  of  Water — Duty  of  Water  in  Different  Countries — 
Measurement  and  Distribution  of  Water — Methods  of 
Irrigation — Cultivation  after  Irrigation — Crops  for  Irri- 
gated Lands— Irrigation  in  Humid  Climates. 

XXII.  ALKALI  LANDS  AND  THEIR  RECLAMATION 278 

Origin  of  Alkali — Kinds  of  Alkali — Effect  on  Physical 
Condition  of  Soil — Vertical  and  Horizontal  Distribution — 
Effect  of  Irrigation  on  Rise  of  Alkali — Effect  of  Alkali  on 
Plants — Limit  for  Germination  and  Growth — Utilization 
and  Reclamation  of  Alkali  Lands — Growing  Alkali- 
resistant  Crops — Retarding  Evaporation — Deep  Plowing 
and  Turning  Under  Alkali — Neutralizing  Black  Alkali — 
Removing  the  Salts  from  the  Soil — Hardpan — Value  of 
Alkali  Land — Alkali  Soils  of  Humid  Regions. 

XXIII.  TEMPERATURE 293 

Sources  of  Soil  Heat — Direct  Radiation  from  the  Sun 
— Precipitation — Chemical  Changes — Physical  Changes — 
Loss  of  Heat — -Radiation — Conduction  into  the  Soil — 
Evaporation  of  Water — -Convection  Currents  of  Air — -Soil 
Temperature  for  Vital  Functions  of  Plants — Tempera- 
ture for  Germination — Temperature  for  Growth — -Tem- 
peratures Favorable  for  Osmosis  and  Diffusion  —Tempera- 
tures for  Nitrification — -Conditions  Affecting  Soil  Tempera- 
ture— Specific  Heat — 'Evaporation  of  Water — Drainage — - 
Presence  of  Water — -Absorption  and  Radiation  of  Heat- 
Latitude  or  Angle  of  Sun's  Rays — Conductivity  of  Soil 
Material  and  Soils — Tillage. 

XXIV.  SOIL  AIR  AND  AERATION 309 

Use  of  Air  in  Soils — -Amount  of  Air  in  Soils — Composition 
of  Soil  Air — Aeration  or  Soil  Ventilation — Water-logged 
Soil — Running  Together. 


viii  CONTENTS 

XXV.  SOIL  ORGANISMS 315 

Macro-organisms — Rodents — Insects — Worms — Plants — 
Micro-organisms — Injurious  Organisms — Beneficial  Organ- 
isms— Distribution  and  Conditions  for  Their  Activity — 
Distribution — Conditions  for  Development — Loss  of  Ni- 
trates— Leaching — Denitnfication. 

XXVI.  TILLAGE 325 

Objects  of  Tillage — Pulverizing  and  Loosening  the  Soil 
— Turning  Under  Vegetable  Matter — Killing  Weeds — 
Storing  and  Conserving  Moisture — Compacting  the  Soil 
— Planting  the  Seed — Implements  of  Tillage — Plows — 
Harrows — Compacters — Seeders — Cultivators — Plowing — 
Time  of  Plowing — Depth  of  Plowing— Dynamiting — Effect 
of  Deep-rooting  Crops — 'Preparation  of  the  Seed  Bed — 
Wheat— Corn— Oats — Cultivation — Value  of  Mulch — 
Root  Injury — Level  Cultivation. 

XXVII.  SOIL  EROSION 358 

Cause  of  Erosion — Effect  of  Topography — Texture  and 
Structure  of  the  Soil — Vegetative  Covering — Character  of 
the  Rainfall — -Results  of  Erosion — Removal  of  Organic 
Matter  and  Nitrogen — Changes  Physical  Character  of 
Soil — Changes  of  Color — Kinds  of  Erosion — Sheet  Erosion 
— Methods  of  Prevention  and  Reclamation— Application 
of  Limestone — Protection  by  Crops — Residues — Increas- 
ing the  Organic  Matter — Deep  Contour  Plowing — Contour 
Seeding  —  Terraces  —  Reforesting  —  Tiling  —  Gullying  — 
Methods  of  Prevention  and  Filling — Straw-brush — Dams 
— Vegetation — Filling  with  Soil. 

XXVIII.  ROTATION 376 

Advantages  of  Rotation — Better  Distribution  of  Work — 
Control  of  Insects  and  Plant  Diseases — Control  of  Weeds — 
Variation  in  Depth  of  Root  Systems — Maintenance  of 
Good  Tilth — Maintenance  of  Organic  Matter — Toxic 
Substances — Increased  Yields — Planning  a  Rotation — 
Places  in  Rotations  for  Crops — Practical  Rotations — Corn 
and  Winter  Wheat  Belt — Cotton  Belt — Hay  and  Pasture 
Province — Spring  Wheat  Region — Great  Plains  Province. 

APPENDIX  I.    SOIL  FERTILITY 389 

Permanent  Agriculture — Are  Soils  Inexhaustible? — Plant 
Food  Elements — Removal  of  Plant  Food—Crop  Require- 
ments— Supply  of  Plant  Food  in  Soils — Nitrogen — 
Phosphorus — Potassium — Other  Elements. 

APPENDIX  II 407 

Average  Yield  of  Crops  Per  Acre  by  States  in  United  States, 
Ten-year  Average,  1906-1915 — Average  Yield  of  Wheat 
Per  Acre  for  Ten  Years,  1905-1914,  United  States  and 
European  Countries. 

APPENDIX  III •> . . .  410 

Farm  Land  Value  Per  Acre — Farm  Property  Value — Corn 
Acreage — Corn  Production — Oats  Production — Spring 
Wheat  Acreage — Winter  Wheat  Acreage — Wheat  Produc- 
tion. 


ILLUSTRATIONS 

FIG-  PAGE 

Map  Showing  the  Soil  Provinces  and  Soil  Regions  of  the  United 
States Frontispiece 

1.  Limestone  Composed  Chiefly  of  Shells  of  Brachiopods 9 

2.  Limestone  Containing  Large  Amounts  of  Crinoid  Stems 9 

3.  Irregular  Weathering  of  Rock  Due  to  Joints  and  Stratification 11 

4.  A  More  Advanced  Stage  of  Weathering 12 

5.  "Capitol  Rock,"  Butte,  Montana 12 

6.  Exfoliated  Granite  in  the  Sierra  Nevadas,  California 13 

7.  Columbia  Glacier  Overriding  a  Forest,  Alaska 14 

8.  Front  of  Columbia  Glacier  in  1910  Compared  in  Height  to  Bunker 

Hill  Monument 15 

9.  The  Material  Carried  and  Rolled  by  Streams  Gives  Them  Their  Great 

Eroding  Power 16 

10.  Inner  Gorge  of  Grand  Canon  of  the  Colorado  River,  Arizona 17 

11.  Wind-carved  Granite 18 

12.  The  Roots  of  Trees  Form  Wedges  for  Prying  Rocks  Apart 19 

13.  Stalactites  and  Stalagmites  Formed  in  a  Cavern  from  Limestone 

Dissolved   by    Carbonated  Water  While    Passing  Through    the 

Rocks  Above 23 

14.  Sinkholes  in  a  Cave  Region — Southern  Illinois 24 

15.  The  Outlets  of  Sinkholes  Sometimes  Become  Clogged  and  "Sinkhole" 

Ponds  Result 24 

16.  Ox-bow  Lakes  Formed  by  Shifting  of  Channel 28 

17.  Typical  Eastern  Swamp  Land 29 

18.  Florida  Everglades 29 

19.  Section  Showing  One  Step  in  the  Filling  of  the  Lake  with  Peat 29 

20.  Hummocks  6  to  12  Inches  High  Found  in  Swampy  Places  Produced 

by  Trampling  of  Stock 30 

21.  Weathering  of  Jointed  Hock  Above  and  Thin  Bedded  Beneath 31 

22.  Rock  Disintegration  and  Formation  of  Talus  Sloj>o 32 

23.  The  Side  of  a  Ravine  Near  Crawfordsville,  Indiana 32 

24.  Mud  Flow 34 

25.  Map  Showing  the  Early  Stages  in  the  Formation  of  Coast  Marshes.  36 

26.  Section  of   Marine   Marsh 36 

27.  Mangrove  Marsh,  Biscayne,  Florida • 37 

28.  Ix-vel  Floor  of  Lake  Chicago,  with  the  Shore-line  in  the  Distance  ...  37 

29.  Terraces  of  Frazier  River  at  Lilloet,  B.  C 38 

30.  Terrace  Along  Creek,  Near  Rockford,  Illinois,  Showing  Stratification  38 

31.  Closer  View  Section  of  Gravel  Terrace  of  Fig.  30 39 

32.  Front  of  Chenega  Glacier  Compared  with  Washington    Monument, 

550  Feet  High 41 

33.  Very  Stony  and  Gravelly  Phase  of  Glacial  Drift   Near  Whitewater, 

Wisconsin 41 

34.  Limestone  Boulder  Showing  Glacial  Scratches,  I'rbana,  111 42 

35.  Glacial  Grooves  or  Stria-  on  Rock  Surface.  Northern  Ohio 43 

36.  Typical  Topography  of  Terminal  Moraine  NmrOromowoc,  Wisconsin  43 

37.  Drumlins — •Remnants  of  Former  Terminal  Moraines 44 

38.  Drumlins — Transverse  View 44 

39.  Adeline  Esker,  Ogle  County,  Illinois 44 

40.  The  Material  Composing  Adeline  Fsker  Consists  of  Coarse  Sand  and 

Gravel. 45 


x  ILLUSTRATIONS 

41.  Map  Showing  Extent  and  Southern  Limit  of  Glaciation  in  North 

America 46 

42.  Map  Showing  the  Three  Centers  of  Ice  Accumulation  in  North 

America 47 

43.  Map  Showing  Extent  of  Ice-sheet,  Europe 48 

44.  A  Section  Showing  the  Black  Sangamon  Soil  with  the  Illinois  Glacial 

Drift  Beneath  and  the  lowan  Loess  Above,  with  the  Present  Soil 
on  the  Surface • 49 

45.  A  Section  Showing  Bloomington  Gravel,  Shelbyville  Till  Sheet,  lowan 

Loess,  Sangamon  Soil,  Silt  Below  Peat 49 

46.  Granite  Boulder  Weighing  About  30  Tons,  at  Depot  of  Northwestern 

R.  R.,  Waukegan,  Illinois 51 

47.  Heap  of  Boulders  Collected  from  a  Moraine  in  Northern  Illinois  ....  51 

48.  A  Dust  Storm  in  Kansas,  May  26,  1912 54 

49.  Sand  Dune  Advancing  Over  Forest,  Beaufort  Harbor,  N.  C 55 

50.  A  Resurrected  Forest,  Dune  Park,  Indiana 55 

51.  Wind  Ripples  on  Sand  Dune 56 

52.  Transplanting  Beach  or  Marram  Grass 56 

53.  The  Grass  in  the  Foreground   Holds  the  Sand  Which  Drifts  from  the 

"Waste"  Beyond  the  Fence 57 

54.  Sand  is  Being  Held  by  Vegetation 57 

55.  Fences  Being  Used  to  Check  the  Movement  of  Sand 58 

56.  Large  "Blowout"  in  Sand  Area,  Mason  County,  Illinois 59 

57.  Black  Locusts  Growing  on  Sand  to  the  Right,  Drifting  Sand  on  Left.  59 

58.  The  Trailing  Wild  Bean  Makes  a  Large  Growth 60 

59.  Pines  Growing  on  Sand  Dunes  in  England 60 

60.  Alluyiation  by  Glacial  Stream,  Below  Hidden  Glacier,  Alaska 62 

61.  Calcium  Carbonate  Concretions  from  the  Loess  of  Illinois 63 

62.  A  Road  Through  a  Deposit  of  Deep  Loess  Along  the  Lower  Illinois 

River 63 

63.  Map  of  United  States,  Showing  Timber  and  Prairie  Areas 76 

64.  Soil  Samplers 119 

65.  Bottle  for  Subsidence  Method  of  Mechanical  Analysis 125 

66.  Nobel's  Elutriator . .  • 126 

67.  Schone's  Elutriator 126 

68.  Hilgard's  Churn  Elutriator • 126 

69.  Machine  for  Centrifugal  Analysis  of  Soils 127 

70.  Yoder's  Centrifugal  Elutriator 127 

71.  King's  Aspirator  for  the  Determination  of  the  Effective  Diameter  of 

Soil  Particles 128 

72.  Shrinkage  of  Different  Types  of  Soil 133 

73.  Cra,cks  in  Black  Clay  Loam  After  a  Long  Dry  Period 136 

74.  Fragments  of  Plants  Found  in  Soils 143 

75.  Fragments  of  Insects  Found  in  Soils 143 

76.  Specimens  of  Charcoal  and  Charcoal-like  Material  Found  in  Soils  146 

77.  Specimens  of  Coal  Found  in  Soils 146 

78.  The  Effect  of  the  Removal  of  Humus  and  of  Wetting  and  Drying 

Upon  Granulation 149 

79.  Arrangement   of   Apparatus   for   Determining   Organic   Matter  by 

Chromic  Acid  Method 155 

80.  Clover  on  Gray  Silt  Loam  on  Tight  Clay 159 

81.  How  Does  This  Man  Handle  Manure? 165 

82.  When  the  Spreader  is  Filled  the  Manure  is  Hauled  to  the  Field 165 

83.  Manure  Spreader  in  Action 167 

84.  An  Expensive  and  Wasteful  Way  of  Handling  Manure  on  the  Farm .  169 

85.  Burning  Corn  Stalks 170 

86.  Adding  Organic  Matter  to  the  Soil  in  the  Form  of  Sweet  Clover 172 


ILLUSTRATIONS  xi 

87.  A .  Showing  Angular  Character  of  Quartz  Particles  in  Decomposed 

Gneiss.     B.  Quartz   Granules  from   Beach   Sand.     C.  Showing 
Outlines  of  Shreds  of  Volcanic  Dust  as  Seen  Under  Microscope .  179, 180 

88.  Diagram  Showing  the  Arrangement  of  Soil  Particles 180 

89.  The  Annual  Rainfall  Over  the  United  States 190 

90.  Soil  Particles  Showing  Films  and  Waists  of  Capillary  Water 200 

91.  Large  and  Small  Bubble  Connected  by  a  Tube 200 

92.  Showing  Theoretically  the  Thickness  of  Films  in  a  Vertical  Soil 

Column 201 

93.  Showing  the  Effect  of  Various  Amounts  of  Organic  Matter  on  the 

Rise  of  Capillary  Water  from  a  Free- water  Surface  for  a  14-day 
Period 208 

94.  Diagram  Showing  the  Relation  of  Different  Forms  of  Moisture  to  the 

Available  and  Unavailable  Moisture  of  Soils 214 

95.  The  Difference   in   Germination  and  Growth  on   Undrained  und 

Drained  Soil 223 

96.  Pipe  Heaved  Nearly  G  Inches  During  Winter  of  1915-1916 225 

97.  Alfalfa  that  was  Completely  Killed  by  Heaving 226 

98.  The  Obstructions  Interfere  with  the  Current  and  Cause  Deflections.  .   227 

99.  Ditch  Gradually  Being  Filled  by  Soil  Due  to  Current  Being  Retarded 

by  Grass 227 

100.  A  Neglected  Ditch  Often  Seen  in  Heavily  Wooded  Areas 227 

101.  Showing  the  Water  Table  with  Lines  of  Tile  Soon  After  the  Insertion 

of  Another  Line 228 

102.  A  Good  Method  of  Conserving  Moisture 234 

103.  Types  of  Rainfall  Over  Dry-farm  Area  of  the  United  States 239 

104.  Sage  Brush  on  Land  Well  Adapted  to  Dry  Farming.   Utah 239 

105.  A  Gravelly  Soil  Not  Well  Adapted  to  Dry  Farming 240 

106.  A  Deep,  Medium-grained  Soil  Well  Adapted  to  Dry  Farming.    Utah .  243 

107.  Campbell  Subsurface  Packer 247 

108.  Turkey  Red  Fall  Wheat,  Without  Irrigation,  Yield  58  Bushels  Per 

Acre .' 249 

109.  White  Hulless  Barley  on  Land  Continuously  Cropped 249 

110.  White  Hulless  Barley  on  Land  Fallowed  the  Previous  Year 249 

111.  Corn  Grown  on  Dry-land  Farm.    Utah 252 

112.  Dry-farm  Potatoes.    Utah 253 

113.  Conduit  for  Conducting  Water  to  Where  it    May   be   Used  for 

Irrigation 258 

114.  Concrete-lined  Canal  that  Permits  no  Loss  by  Seepage 258 

115.  Roosevelt  Dam,  Salt  River,  Arizona 260 

116.  Granite  Reef  Diversion  Dam,  Salt  River  Project.  Arizona 260 

117.  Desert  Lands  and  Homestead,  Huntloy  Project,  Montana 261 

118.  Wheat  Field,  Minidoka  Project,  Idaho' .201 

119.  Chains  for  Puddling  the  Mud  of  Canals  to  Prevent  Set-page 267 

120.  Rectangular  Weir 268 

121.  Trapezoidal  or  Cippoletti  Weir,  Showing  Method  of  Dividing  the 

Stream 269 

122.  Basin  or  Check  System  of  Irrigating  Orchards 270 

123.  Irrigating  Potatoes  by  Furrows .271 

124.  Method  of  Irrigating  by  Overhead  Sprays 

125.  Mallin  Ranch,  Salt  River  Project,  Arizona.  . 

126.  Alfalfa  Field,  Yuma  Project,  Arizona '. 274 

127.  Beginning  of  an  Alkali  Sjx>t .  . 

128.  Alkali  Area  Showing  the  Absence  of  Vegetation. 

129.  Apricot  Trees.    The  Scanty  Foliage  Shows  the  Kffoct  of  Alkali.    .  .   283 

130.  An  Orchard  Well  Cultivated  Prevents  the  Rise  of  Alkali 286 


rii  ILLUSTRATIONS 

131.  Growth  of  Barley  on  Partly  and  Fully  Reclaimed  Alkali  Land 288 

132.  Wheat  on  Reclaimed  Alkali  Land  Near  Fresno,  Gal 289 

133.  A  Dwarfed  Bushy  or  Leafy  Corn  Plant  Growing  on  Alkali  Soil  of 

Humid  Area 291 

134.  Difference  in  Growth  on  Light  and  Dark  Colored  Soils 303 

135.  Showing  the  Comparative  Areas  Covered  by  the  Sun's  Rays  When 

Vertical,  30,  60  and  80  Degrees  from  the  Vertical 304 

136.  Effect  of  Slope  on  the  Area  Covered  by  the  Sun's  Rays 305 

137.  Diagram  Showing  the  Theoretical  Action  of  the  Plow 327 

138.  Showing  the  Three  Types  of  Mold-boards 327 

139.  Plow  with  Separate  Jointer  and  Rolling  Coulter  Attached  Ready  for 

Use 328 

140.  The  Combined  Jointer  and  Rolling  Coulter 329 

141.  Disk  Plow 329 

142.  Lister  for  Preparing  the  Ground  and  Planting  Corn 330 

.  143.  Work  Done  by  Lister 331 

144.  Subsoil  Plow 331 

145.  Spike-tooth  Harrow 332 

146.  Spring-tooth  Harrow 332 

147.  Acme  Blade  Harrow 333 

148.  The  Solid  Disk 333 

149.  The  Cut-away  Disk 334 

150.  The  Spading  Disk  Harrow 334 

151.  Smooth  or  Drum  Roller 335 

152.  The  Culti-packer,  a  Form  of  Corrugated  Roller,  Showing  Work  Done  336 

153.  Disk  Drill  and  Its  Work 336 

154.  Press  Drill 337 

155.  Ordinary  Corn  Planter  with  Attachment  for  Planting  Cowpeas  in 

Hill  or  Row  with  Corn 338 

156.  Three-shovel  Cultivator 338 

157.  Disk  Cultivator 339 

158.  Surface  or  Blade  Cultivator  with  Leveler • 339 

159.  Weeder 340 

160.  An  Early  Form  of  Plow 340 

161.  The  Sod  is  Well  Turned  and  Represents  Good  Wo:  k 341 

162.  Good  Plowing  in  Stubble  Land 342 

163.  A  Crooked  Furrow  Does  Not  Look  Well 342 

164.  Previous  to  Plowing,  Disking  Should  be- Done 344 

165.  Grain  Produced  from  Five  Tenth-acre  Plots  Prepared  in  Different 

Ways  for  Winter  Wheat 346 

166.  A  Good  Seed  Bed  on  Stalk  Ground 348 

167.  Nine-year  Average  Yield  43.3  Bushels  Per  Acre. ' 351 

168.  Nine-year  Average  Yield  48.9  Bushels  Per  Acre 351 

169.  Nine-year  Average  Yield  7.4  Bushels  Per  Acre 351 

170.  Yields  of  Corn  (Field  Weight)  with  Different  Methods  of  Tillage.  .  354 

171.  Yield  of  Corn  (Field  Weight)  with  Different  Method  of  Tillage. ...  354 

172.  Level  Cultivation 355 

173.  Ridged  Cultivation  with  Drilled  Corn 356 

174.  Two  Hundred  Square  Miles  of  Once  Forested  Mountains  in  China.  .  359 

175.  Sweet  Clover  on  Badly  Eroded  Land 361 

176.  Cultivated  Terraces  in  China 364 

177.  Guide-row  Terraces 365 

178.  Level-bench  Terrace 366 

179.  A  Terraced  Park  in  Mississippi 367 

180.  The  Mangum  Terrace 367 

181.  Locusts  Growing  on  Gullied  Land 368 


ILLUSTRATIONS  xiii 

182.  Erosion  in  Pasture  Near  Crest  of  Slope 370 

183.  Old  Field  Erosion  in  Mississippi 370 

184.  Old  Erosion 371 

185.  Brush  Checking  Erosion 372 

186.  Headwater  Erosion 372 

187.  Earth-darn  for  Checking  Erosion 372 

188.  Filling  a  Gully  by  Means  of  a  Concrete  Dam 373 

189.  Agricultural  Provinces '. 383 

190.  Wheat  Growing  on  a  Soil  Very  Deficient  in  Nitrogen 397 

191.  Legumes  Turned  Under  Have  the  Same  Effect  as  the  Addition  of 

Nitrogen 397 

192.  Wheat,  1911,  Urbana  Field 401 

193.  Wheat,    1911,    Urbana    Field.      Finely    Ground    Rock    Phosphate 

Applied 401 

194.  Corn  on  Peaty  Swamp  Land,  1903 404 

195.  Farm  Land,  Value  Per  Acre,  1910 410 

196.  Farm  Property,  Value,  1910 411 

197.  Corn  Acreage,  1909 412 

198.  Corn  Production,  1909 413 

199.  Oats  Production,  1909 414 

200.  Spring  Wheat  Acreage,  1909 415 

201.  Winter  Wheat  Acreage,  1909 416 

202.  Wheat  Production,  1909 417 


SOIL    PHYSICS  AND 
MANAGEMENT 

CHAPTER  I 
SOIL  MATERIAL  AND  ITS  ORIGIN 

Definition  of  Soil. — The  land  surface  of  the  earth  is  covered 
almost  everywhere  with  a  layer  of  unconsolidated  material  de- 
rived from  rocks  by  the  processes  of  weathering.  This  stratum 
varies  in  thickness  from  a  few  inches  to  hundreds  of  feet  and  may 
even  be  absent  from  small  areas,  not  because  it  was  never  formed 
there,  but  because  it  has  been  carried  away.  The  agencies  of  trans- 
portation have  done  so.  much  work  that  in  many  instances  much 
or  all  of  the  loose  material  covering  the  rocks  was  not  derived 
from  those  beneath,  but  from  rocks  at  some  distance,  even  hundreds 
of  miles  away.  This  material  varies  in  composition  with  the  rock 
from  which  it  was  derived  and  the  agencies  producing  it.  It  cannot 
be  termed  a  soil  until  organisms  have  worked  upon  it,  modifying 
it  to  a  greater  or  loss  extent.  The  depth  of  the  layer  upon  which 
the  organisms  have  acted  is  only  a  few  feet. 

From  its  origin,  a  soil  may  be  defined  as  disintegrated  and 
decomposed  rock  mixed  with  more  or  less  organic  matter,  while 
from  its  use  it  is  defined  as  that  part  of  the  ea rib's  surface  adapted 
to  the-  mechanical  support  and  nourishment  of  plants. 

Elements  of  the  Earth's  Crust. — The  earth  has  been  studied 
by  various  means  and  the  composition  determined  to  a  depth  of 
approximately  twenty  miles.  Of  the  elements  known,  comparatively 
few  occur  in  any  large  quantities  in  this  stratum.  Eight  constitute 
about  08.. 5  per  cent.  The  following  table  shows  the  relative  abun- 
dance of  these  elements. 

Soil  Forming  Minerals. — Aside  from  oxygen  and  nitrogen  as 
air,  and  carbon  as  graphite  or  diamond,  these  elements  rarely  ever 
exist  in  a  free  state,  but  are  found  in  combinations  as  minerals. 
These  are  natural  substances,  possessing  definite  physical  charac- 
teristics as,  specific  gravity,  hardness,  brittleness.  color,  cleavage, 
and  sometimes  crystalline  form  and  having  a  more  or  less  definite 
chemical  composition. 

1 


SOIL  PHYSICS  AND  MANAGEMENT 

A  verage  Composition  of  the  Known  Earth  l 


Elements 

Lithosphcre  t 
93  per  cent 

Hydrosphere  J 
7  per  cent 

Average, 
including 
atmosphere 

Oxygen  *.  .  . 

4733 

8579 

5002 

Silicon  

27.74 

•V,  Ml 

Aluminum  

7.85 

7.30 

Iron  

450 

4.18 

Calcium  

347 

.05 

3.22 

Magnesium  

224 

.14 

2.08 

Sodium  

2.46 

1.14 

2.36 

Potassium  

2.46 

.04 

2.28 

Hydrogen  

.22 

10.67 

.95 

Titanium  

.46 

.43 

Carbon  

.19 

002 

.18 

Chlorine  

.06 

2.07 

.20 

Bromine  

.008 

Phosphorus  

.12 

.11 

Sulfur  

12 

09 

.11 

Barium  

.08 

.08 

Manganese  

.08 

.08 

Strontium  

.02 

.02 

Nitrogen  

.03 

Fluorine  

.10 

.10 

All  other  elements  

.50 

.47 

100.00 

100.00 

100.00 

*  The  elements  essential  for  crops  are  in  bold  type, 
t  The  solid  part  of  the  earth's  crust, 
j  The  liquid  part,  oceans,  seas,  etc. 

The  hardness  of  minerals  is  indicated  by  the  following  scale: 
(1)  talc — finger  nail  scratches  it  easily;  (2)  gypsum — thumb  nail 
scratches  slightly;  (3)  calcite — can  be  scratched  by  common  soft 
pin;  (4)  fluorite — soft  iron  scratches  it;  (5)  apatite — scratched 
by  a  good  knife;  (6)  feldspar — very  hard  knife  scratches  it;  (7) 
quartz — scratches  glass;  (8)  topaz — scratches  quartz;  (9)  corun- 
dum— sera tx-hes  topaz ;  (10)  diamond. 

The  number  of  minerals  that  form  soils  is  not  large,  but  they 
may  be  found  in  many  intermediate  stages  because  the  process  of 
decomposition  is  a  gradual  one. 

1.  Quartz,  silica  (Si(X)  is  a  very  abundant  mineral  in  rocks 
and  the  most  abundant  in  soils.  When  crystalline  it  possesses  a 
glassy  appearance  and  is  transparent  in  thin  slices,  but  impurities 
render  it  more  or  less  opaque.  The  common  crystalline  varieties 
are  quartz  crystal,  rose,  smoky  and  milky  quartz.  The  non-crys- 
talline varieties  are  usually  opaque  and  include  flints,  cherts, 
chalcedony  and  the  different  forms  of  agate.  In  rocks  such  as 


SOIL  MATERIAL  AND  ITS  ORIGIN 


granite,  quartz  occurs  as  glassy  masses  which  do  not  decompose  as 
most  other  minerals  do,  but  remain  as  distinct  grains  of  quartz 
when  the  rock  is  broken  down.  In  limestones  it  frequently  occurs 
as  chert,  an  impure  rather  soft  form,  or  as  flint.  Sand,  sandstones, 
and  quartzite  are  formed  principally  of  quartz.  The  fact  that  its 
hardness  is  7,  that  it  is  almost  insoluble,  decomposes  very  slowly  and 
possesses  no  cleavage,  makes  it  very  abundant  among  the  coarser 
constituents  of  soils.  It  may  be  distinguished  by  its  glass-like  ap- 
pearance, hardness,  shell-like  fracture,  lack  of  cleavage  and  its 
resistance  to  the  action  of  all  acids  with  the  exception  of  hydro- 
fluoric. 

2.  Feldspars. — The  feldspars  include  double  silicates  of  potas- 
sium, sodium,  calcium  and  aluminum.  They  possess  a  hardness  of 
6,  distinct  cleavage  and  decompose  rather  readily  in  the  presence 
of  carbonated  water.  The  action  of  carbonic  acid  is  to  dissolve 
out  the  base  or  bases,  forming  the  soluble  carbonates,  leaving  a 
hydrated  aluminum  silicate,  kaolin,  and  finely  divided  free  silica 
which  constitute  the  clay  of  soils.  The  process  is  known  as  kaolin- 
ization.  The  following  table  gives  the  composition  of  the  principal 
feldspars. 

Composition  of  Principal  FcUlxpurs  2 
Per  cent 


Varieties 

SiOj 

AliO. 

KsO 

NaiO 

CaO 

Orthocla.sc   

64.7 

18.4 

169 

1 

Albitc  

.  .  .  i      68.0 

20.0 

12.0 

Oligocla.se  

.  .  .       62.0 

24.0 

9.0 

o.O 

Labradoritc  

.  .  .  I      53.0 

30.0 

4.0 

13.0 

Anorthitc           

.  .  .       43.0 

37.0 

20.0 

As  an  illustration  of  the  decomposition  of  feldspar,  ortboclase 
may  be  taken.  Carbonated  water  coining  in  contact  with  this  min- 
eral dissolves  out  the  potassium,  forming  potassium  carbonate,  which 
being  soluble  is  carried  away.  In  the  process  the  excess  of  silica, 
which  amounts  to  approximately  -0  per  cent  in  orthoclase^is  sepa- 
rated as  extremely  fine  particles  most  of  which  are  classed  as  clay. 
The  alumina  is  left  in  combination  with  silica  as  a  hydrous  alumi- 
num silicate  forming  the  mineral  kaolin  which  also  constitutes  clay. 
The  result  then  of  the  decomposition  of  feldspar  is  a  light-colored 
clay  composed  of  free  silica  and  kaolin. 

3.  Amphibole  and  Pyroxene. — These  groups  of  minerals  are 


4  SOIL  PHYSICS  AND  MANAGEMENT 

very  abundant  in  some  rocks  and  vary  a  great  deal  in  composition 
and  physical  properties.  They  have  about  the  same  hardness  as 
feldspar  and  possess  more  or  less  definite  cleavage  planes.  They 
may  be  either  aluminous  or  non-aluminous.  Magnesium,  calcium 
and  iron  are  nearly  always  present.  The  iron  is  frequently  in  the 
ferrous  condition.  As  a  general  rule  these  groups  of  minerals 
decompose  somewhat  readily,  giving  rise  to  hydrous  magnesium 
silicates  and  soluble  carbonates,  the  latter  of  which  are  carried  away 
in  solution.  The  hydrous  magnesium  silicate  may  be  in  the  form 
of  serpentine  or  talc,  the  latter  of  which,  because  of  its  softness,  is 
readily  broken  down  into  clay.  The  ferrous  iron  present  becomes 
oxidized  and  generally  gives  a  yellow  or  brownish  color  to  the  soil 
formed.  As  these  groups  of  minerals  are  frequently  magnesian,  the 
soil  resulting  is  not  generally  highly  productive. 

4.  Muscovite — White   Mica. — This   mineral   is  made  up  of 
transparent  laminae  or  folia  possessing  a  hardness  of  2  to  2.5.    These 
folia  are  thin,  elastic  and  tough. 

The  chemical  composition  and  physical  properties  of  this  min- 
eral seem  to  indicate  that  it  would  decompose  rather  readily,  but 
on  the  other  hand  it  is  very  stable  and  resists  decomposition  so 
well  that  in  most  cases  the  mica  remains  in  the  residue  as  distinct 
shining  flakes,  giving  the  soil  a  peculiar  glittering  appearance 
where  the  flakes  are  of  considerable  size.  The  first  step  in  its  de- 
composition is  hydration,  resulting  in  a  Hydra  ted  mica  having  a 
pearly  luster.  When  decomposition  is  complete  the  product  is  the 
hydrous  aluminum  silicate  or  clay.  Muscovite  is  found  in  granites 
to  a  considerable  extent,  but  is  not  very  often  associated  with  the 
more  basic  rocks  or  those  containing  a  large  per  cent  of  magnesium, 
calcium  or  iron. 

5.  Biotite — Black  Mica. — Biotite  differs  from  the  preceding 
inica  in  color,  and  in  the  fact  that  it  decomposes  more  readily.    It 
contains  aluminum  and  iron  in  both  ferrous  and  ferric  states  with 
both  magnesium  and  potassium.     It  decomposes  into  a  mixture  of 
hydrated  aluminous  and  magnesian  silicates,  both  of  which  con- 
stitute clay.    Biotite  occurs  associated  with  the  more  basic  rocks. 

6.  Zeolites. — The  zeolites  comprise  a  group  of  secondary  min-    *  . 
crals  of  somewhat  doubtful  importance,  whose  _f  unction,  it  is  be-    , 
lieved,  is  to  retain  the  potassium  and  calcium  in  the  soil  against 
leaching.     In  the  decomposition  of  minerals  to  form  soil  material 
the  potassium,  sodium  and  calcium  unite  with  the  aluminum  ami 
silica  in  loose  combinations  instead  of  being  carried  away  in  solu- 


SOIL  MATERIAL  AND  ITS  ORIGIN  5 

tion  and  lost.  From  these  combinations  the  elements  are  liberated 
somewhat  as  needed  by  plants.  The  minerals  of  this  group  are  de- 
composed by  hydrochloric  acid  with  the  separation  of  colloidal 
silica. 

The  preceding  minerals  are  silicates,  but  there  are  a  few  non- 
silicates  that  should  be  considered  in  the  study  of  soils. 

7.  Calcite  (CaCO3). — Calcite  is  a  very  common  mineral  exist- 
ing as  limestone  and  marble.     Its  composition  is  CaO,  5(i  per  cent, 
and  C02,  44  per  cent,  when  pure.    It  possesses  a  hardness  of  about 
3,  distinct  cleavage  and  is  soluble  in  carbonated  water,  one  part  in 
1020  of  water,  forming  the  bicarbonate   (CaH2(C03)2).     In  the 
formation  of  soil  material  from  rock  made  up  largely  of  calcium 
carbonate,  the  insoluble  impurities  are  left  and  form  the  soil.    As  a 
general  rule  limestone  soils  are  quite  fertile. 

8.  Dolomite  (CaMg(C03)2). — The  hardness  of  dolomite  is  3.5. 
It  is  composed  of  54.35  per  cent  of  calcium  carbonate  and  45.05  per 
cent  of  magnesium  carbonate.     Dolomitic  limestone  is  made  up  of 
these  minerals,  though  probably  not  always  in  these  proportions.    It 
is  slowly  soluble  in  carbonated  water,  leaving  the  impurities  to  form 
soil  material.    A  large  amount  of  magnesium  carbonate  is  injurious 
to  some  crops  and  constitutes  much  of  the  alkali  in  soils  of  humid 
areas. 

9.  Gypsum  (CaS04.2H20). — Cypsum  possesses  a  hardness  of 
2  and  the  following  composition  :   sulfur  trioxid,  40.5  per  cent,  lime 
32.0  and  water  20.9  per  cent.    It  is  found  in  considerable  quantities 
in  arid  regions  where  salt  lakes  formerly  existed,  but  is  of  compara- 
tively little  importance  as  a  soil  former,  since  the  soil  derived  from 
it  has  very  little,  value.     It  has,  however,  some  value  as  a  remedy 
for  black  alkali  that  is  so  frequently  found  in  arid  and  semi-arid 
regions. 

10.  Apatite    (Oa-(P04).tri). — This   mineral    is   important   in 
soils  because  of  the  phosphorus  it  furnishes.     Fortunately  it  exists 
in  all  rocks,  though  in  very  small  amounts,  and  when  these  decom- 
pose very  little  of  the  phosphorus  is  lost  through  solution.     Hence 
a  soil  will  usually  show  a  higher  per  cent  of  phosphorus  than  the 
original  rock.    In  some  cases  the  chlorine  is  replaced  by  fluorine. 

11.  Limonite   (2I«Y,O:,.:MI,(>)   and   Hematite  (Fo.,0.,).— Sev- 
eral other  minerals  might  be  mentioned,  among  which  are  limonite, 
the  hydrated  ferric  oxide  having  85. 0  per  cent  of  Fe,O.t  and  14.4  per 
cent  of  water,  and  hematite  30  per  cent  of  oxygen  and  70  per  cent 
of  iron.    One  or  the  other  of  these  and  sometimes  both  arc  found  in 


6  SOIL  PHYSICS  AND  MANAGEMENT 

nearly  all  soils  giving  the  characteristic  iron  color,  the  former  im- 
parting a  yellowish  or  brownish  yellow  color  while  the  latter  gives 
a  decidedly  reddish  color.  Varying  proportions  of  these  mixed 
together  give  many  shades  of  red,  brown  and  yellow. 

12.  Magnetite  (Fe:,04)  or  (FeO.  Fe203). — Magnetic  iron  ore 
or  magnetite  exists  in  nearly  all  igneous  rocks -in  small  quantities 
but  in  some  in  sufficient  amounts  to  form  a  very  important  soil  con- 
stituent. It  does  not  decompose  very  readily,  but  remains  as  black 
magnetic  particles  in  the  soil.  Black  sands  of  some  parts  of  North 
Carolina  and  some  of  the  alluvial  soils  of  California  contain  this 
mineral.  It  may  be  easily  recognized  by  its  magnetic  properties. 
Like  quartz  sand  it  is  inert  and  soils  formed  largely  of  this  mineral 
would  be  very  poor. 

ROCKS 

Rocks  are  masses  of  minerals  or  mineral  aggregates  and  are 
divided  into  three  classes,  igneous,  those  formed  through  the  agency 
of  heat,  aqueous,  those  formed  through  the  agency  of  water,  and 
metamorpliic,  where  igneous  or  aqueous  rocks  are  changed  through 
one  or  both  of  these  agencies  into  different  forms,  but  having  prac- 
tically the  same  chemical  composition. 

1.  Igneous  rocks  are  divided  into  two  groups,  first,  intru- 
sive or  plutonic,  those  formed  at  considerable  depth  in  the  earth's 
crust  where  they  cooled  with  sufficient  slowness  to  crystallize,  and 
later  exposed  through  erosion;  second,  eruptive  or  volcanic,  those 
thrown  out  on  the  surface  of  the  earth  through  volcanic  agencies. 
Both  classes  of  igneous  rocks  are  formed  by  the  fusing  and  mixing 
of  rocks,  such  as  limestones,  shales  and  sandstones,  due  to  the  heat 
developed  in  the  folding  of  the  earth's  crust  in  its  adjustment  to 
the  shrinking  interior.  After  the  adjustment  takes  place,  this 
molten  mass  gradually  cools,  the  minerals  crystallize,  forming  the 
group  of  crystalline  rocks.  In  this  folding,  if  a  fracture  should 
occur  extending  to  the  surface  of  the  earth,  much  of  this  molten 
mass  may  be  forced  out  on  the  surface  and  constitute  the  volcanic 
rocks.  This  may  cool  rapidly  and  solidify  into  a  glassy  or  semi-crys- 
talline condition.  In  some  cases  the  violence  of  the  explosion  that 
frequently  accompanies  volcanoes  throws  immense  masses  of  this 
material  into  the  air, which  falls  in  the  form  of  ash  in  the  vicinity 
of  the  volcano,  but  sometimes  as  dust  is  carried  over  large  areas  of 
the  earth's  surface  by  air  currents.  The  igneous  rocks  are  divided 
into  several  groups  according  to  their  mineral  composition. 


SOIL  MATERIAL  AND  ITS  ORIGIN  7 

(a)  Granite-Rhyolite. — This   group   is   composed   of   quartz, 
feldspars,  chiefly  orthoclase  and  albite,  mica,  either  hlack  or  white, 
and  ampliibole  or  pyroxene.    A  small  amount  of  apatite  is  always 
present.    Rhyolite  is  the  principal  volcanic  rock  of  this  group.     In 
the  decomposition  of  this  group  carbonated  water  attacks  the  feld- 
spars, dissolving  out  the  potassium  and  sodium  in  the  form  of  car- 
bonates, leaving  the  clay  residue.    The  quartz  is  broken  down  into 
sand  and  gravel  while  the  other  minerals  are  decomposed  into  other 
products  as  given  under  those  special  minerals  above.    The  resulting 
soil  material  formed  is  a  sandy  clay,  the  color  depending  upon  the 
amount  of  iron-bearing  minerals  in  the  granite.    The  soil  material 
formed  from  rhyolites  and  other  volcanic  granites  differs  only  in 
fineness  from  that  resulting  from  intrusive  granites. 

(b)  Syenite-Trachyte. — This    group    consists   chiefly   of    the 
feldspars,  orthoclase  or  albite,  minerals  of  the  mica,  amphibole  or 
pyroxene  groups  and  a  small  amount  of  apatite.    It  ditfcrs_from  the 
granites  jn  the  absence  of  quartz.     Its  decomposition  is  simJlar^o 
that  of  the  granite  but  gives  a  clay  free  from  sand,  colored  by  iron 
compounds.     This  rock  is  not  so  common  as  granites.     Trachyte  is 
the  volcanic  form  of  syenite. 

(c)  Diorite-Andesite. — These  rocks  contain  oligoclase,  mica, 
usually  biotite,  amphibole  or  pyroxene  and  apatite.     Quartz  may 
be  present.     The  soil  material  formed   is  cither  a  rather  highly 
colored  clay  or  sanely  clay,  depending  on  the  absence  or  presence  of 
quartz  in  the  original  rock.    Andesite  is  a  common  volcanic  form. 

(d)  Diabase-Basalt. — This  group  of  rocks  consists  of  labrado- 
rite,  amphibole  or  pyroxene,  usually  the  latter,  and  small  amounts  of 
apatite.    Quartz  may  be  present  in  small  quantities  as  in  the  case  of 
the  diorites.    Usually  large  amounts  of  magnesium  and  iron-bearing 
minerals  are  present.     The  decomposition  of  this  group  gives  a 
highly  colored  clay  containing  large   amounts  of  hydrated   mag- 
nesium silicates.    Basalt  is  the  volcanic  form. 

Other  groups  of  igneous  rocks  might  be  given,  but  these  are 
sufficient  to  illustrate  the  changes  that  take  place  in  the  formation 
of  soil  material  from  them. 

2.  Aqueous  rocks  are  divided  into  three  classes,  (a)  those 
whose  constituents  have  been  in  solution  and  have  been  deposited 
by  cooling,  evaporation,  release  of  pressure  or  by  direct  chemical 
precipitation;  (b),  sedimental  or  fragrnental  deposits,  those  formed 
by  the  breaking  down  of  preexisting  rocks  and  deposited  by  the 
action  of  water;  and  (c),  those  formed  largely  by  plants  and 


8  SOIL  PHYSICS  AND  MANAGEMENT 

animals.    It  is  quite  impossible  to  draw  any  distinct  lines  between 
the  groups. 

(a)  Chemical  Precipitates. — Rocks  formed  in  this  way  are  not 
of  a  great  deal  of  importance  as  soil  formers,  but  have  great  eco- 
nomic value.     These  include  the  precious  stones,  the  ores  both  of 
useful  and  precious  metals  and  deposits  of  plant  food,  especially 
potassium  and  phosphorus. 

(b)  Sedimentary    or    Fragmental. — This    division    includes 
sandstones  and  shales.    Sandstones  may  be  divided  into  classes  ac- 
cording to  the  material  that  cements  the  particles  together,  as 
siliceous,  ferruginous,  or  calcareous.     Siliceous  sandstones  break 
down  largely  through  physical  or  mechanical  agencies,  forming  a 
sandy  soil  of  unusually  low  agricultural  value.    A  good  example  of 
this  is  the  St.  Peter's  sandstone  of  northern  Illinois.    Ferruginous 
sandstones  are  broken  down  in  a  way  similar  to  the  siliceous,  except 
that  chemical  agents  are  more  apt  to  affect  the  cementing  material. 
The  resulting  soil  is  a  sand,  colored  by  compounds  of  iron  and  does 
not  possess  a  high  degree  of  fertility.     In  the  breaking  down  of 
calcareous  sandstones,  the  lime  is  dissolved  out  by  the  action  of 
carbonated  water,  thus  freeing  the  particles,  and  forming  a  rather 
poor  sandy  soil.     The  decomposition  of  felspathic  sandstones  may 
give  rise  to  soils  of  fair  fertility  because-  of  the  potassium  and  lime 
present,  but  on  the  other  hand  micaceous  sandstones  produce  soils 
of  low  value. 

Shales  vary  largely  in  physical  composition.  Some  are  composed 
of  clay  while  others  contain  much  coarser  material,  such  as  silt  or 
even  sand.  The  indurated  character  of  shales  is  principally  due  to 
pressure  and  they  are  consequently  easily  broken  down  into  soil 
material.  The  stratification  also  aids  this  process.  The  soils  formed 
from  shales  vary  from  very  heavy  clay  to  silty  or  sandy  ones,  and 
may  be  extremiely  difficult  to  work.  In  general  shale  soils  are  not 
of  high  agricultural  value. 

(c)  Organic. — This   includes  those  deposits   that  have  heen 
formed  through  the  agency  of  organisms.     They  consist  of  coal, 
chalk,  marl,  and  limestone. 

Calcareous  rocks  include  chalk,  marl,  and  the  various  limestones 
(Fig.  1.)  Soils  are  formed  from  these  through  the  solvent  power  of 
carbonated  water  which  removes  the  lime  and  magnesia  as  the 
bicarbonate,  leaving  the  insoluble  impurities  as  soil  material.  This 
may  consist  of  particles  of  sand  or  quartz  or  some  of  the  finest  soil 
constituents  as  silt  or  clay  (Fig.  2).  Limestones  frequently  con- 


SOIL  MATERIAL  AND  ITS  ORIGIN  9 

tain  masses  of  chert,  impure  quartz,  or  flint  which  may  constitute 
no  small  part  of  the  soil,  thus  giving  rise  to  cherty  or  llinty  soils. 
The  rapidity  with  which  a  soil  is  formed  from  a  limestone  depends 


Fio.  1. — Limestone  composed  chiefly  of  shells  of  Brachiopods.     (Church.) 


Fro.  2. — Limestone  containing  large  amounts  of  Crinoid  stems.      (Church.) 

upon  the  amount  of  impurities  present.  A  limestone  containing 
two  per  cent  of  impurities  could  leave  approximately  two  feet  of 
residue  for  each  100  feet  of  limestone  removed  in  solution  provided 
nothing  is  lost  hy  erosion.  Limestone  soils  are  usually  fertile. 


10  SOIL  PHYSICS  AND  MANAGEMENT 

3.  Metamorphic  rocks  include  those  that  have  been  changed 
from  their  original  condition  by  both  physical  and  chemical  agen- 
cies. These  may  have  been  of  either  aqueous  or  igneous  origin. 
Changes  have  given  rise  to  marbles  from  limestones,  slates  from 
shales,  and  gneisses  and  schists  from  igneous  rocks. 

QUESTIONS 

1.  Define  soil. 

2.  Which  of  the  elements  essential  for  crops  are  taken  from  the  air  and 

which  from  the  soil? 

3.  What  is  the  significance  of  the  hardness  of  a  mineral  in  the  formation  of 

soils? 

4.  Why  should  quartz  be  such  a  common  constituent  of  soils? 

5.  Why  is  little  feldspar  found  in  soils  when  it  is  so  abundant  in  rocks? 

6.  What  is  the  chief  value  of  zeolites? 

7.  What  is  the  importance  of  non-silicates  as  soil  formers? 

8.  Which  are  the  principal  non-silicate  minerals  in  soils  of  humid  regions? 

9.  How  are  igneous  rocks  formed? 

10.  Give  distinctions  between  granites,  syenites,  diorites,  and  diabases. 

11.  Distinguish  between  chemical  precipitates  and  sedimentary  rocks. 

12.  How  are  soils  formed  from  calcareous  rocks? 

13.  Where  do  we  find  soils  formed  from  chalk?     From  limestone? 

REFERENCES 

1  Clark,  F.  W.,  Bulletin  616  U.  S.  Geological  Survey,  The  Data  of  Geo- 
chemistry, 1916,  p.  34. 
•Merrill,  G.  P.,  Rocks,  Rock- Weathering  and  Soils,  1906,  p.  15. 


EOCKS  are  broken  down  into  soil  material  through  the  processes 
of  weathering  (Figs.  3,  4,  and  5).  These  may  be  divided  into  (1) 
physical  agencies  that  break  the  rock  into  smaller  pieces  without 
affecting  it  chemically,  and  (2)  chemical  agencies  that  change  the 
composition  of  the  minerals  forming  the  rock  and  in  so  doing  exert 


' 
I 

. 


. 

••_ 


Fio.  3. — Irregular  weathering  of  rock  due  to  Joints  and  stratification.     Note  talus  at  base. 
(Chamberlain  tind  Salisbury,  Courtesy  Henry  Holt  A  Co.) 

a  marked  influence  upon  its  physical  character.  The  work  of  the 
physical  agencies  is  disintegration,  while  that  of  the  chemical  agen- 
cies is  decomposition.  Each  is  accompanied  and  aided  by  the  other 
in  its  work  and  the  changes  tend  to  produce  more  stable  forms  under 
existing  conditions.  As  an  illustration,  feldspars  are  not  very  stable 
minerals  under  ordinary  conditions,  and  hence  break  down  into 
substances  that  are  more  stable.  The  chemical  changes  produce 
hydrous  aluminum  silicate,  carbonates  and  free  silica  which  are 
much  more  stable  than  the  feldspar  from  which  they  are  derived. 
Physically,  the  clay  is  much  more  stable  than  the  original  mineral 

11 


12 


SOIL  PHYSICS  AND  MANAGEMENT 


or  even  the  coarse  soil  constituents  because  it  has  approached  more 
closely  the  limit  of  mechanical  division.  The  others  may  be  broken 
down  into  smaller  fragments  by  the  agencies  of  weathering. 

1 


Fia.  4. — A  more  advanced  stage  of  weathering  than  Fig.  3.     (Chamberlain  and  Salisbury, 
Courtesy  Henry  Holt  &  Co.) 


Fio.  5. — "Capitol  Rock,"  Butte,  Montana.     The  different  levels  are  due  to  varying  hard- 
ness of  the  rock  strata. 

I.    PHYSICAL  AGENCIES. 

(a)  Heat  and  Cold. — In  general,  substances  expand  when 
heated  and  contract  when  cooled.  This  is  true  of  rocks.  They  are, 
however,  poor  conductors  of  heat  and  the  high  temperature  of  the 


WEATHERING 


13 


rock  extends  to  only  a  slight  depth.  The  greater  expansion  of  the 
surface  produces  a  strain  that  frequently  causes  a  layer  to  break  off, 
sometimes  with  considerable  violence  (Fig.  <>).  In  Ixnver  Cali- 
fornia, slabs  as  much  as  ten  feet  long  and  from  eight  to  ten  inches 
thick  have  been  observed  on  the  southwest  side  of  rock  exposures 
that  were  produced  in  this  way.  Many  similar  cases  may  be  seen  in 
the  arid  regions  in  southwestern  United  States.  Boulders  are  some- 
times found  in  this  latitude  that  show  peculiar  exfoliation  due  to 
unequal  heating.  This  action  is  more  noticeable  in  fine-grained 


Fia.  6. — Exfoliated  granite  in  the  Sierra  Nevada*,  California.  Previous  glaeiation 
has  removed  the  loose  material,  giving  the  njtenry  of  heat  a  better  rhance.  Korks,  Hock- 
Weathering  and  Soils,  Merrill.  (Courtesy  The  Macniillan  Company.) 

than  in  coarse-grained  rocks,  and  in  higher  altitudes  where  the  tem- 
perature changes  are  great  and  sudden.  \V.  11.  Bartlett  '  lias  shown 
that  granite  expands  or  contracts  .(HXMXM.s  of  an  inch  per  foot  for 
each  degree  Fahrenheit.  Marble  changes  .<MI<M>I>:><;,  while  sandstone 
changes  .()()()()()!».">  of  an  inch  per  degree.  Practical  applications  of 
this  principle  have  sometimes  been  made  in  quarrying  and  in  re- 
moving rocks  in  constructing  roads.  Boulders  may  be  broken  up  by 
heating  and  cooling  suddenly.  K'ocks  are  made  up  of  various  min- 
eral crystals  that  possess  different  coefficients  of  expansion.  The 


14 


SOIL  PHYSICS  AND  MANAGEMENT 


repeated  differential  expansion  and  contraction  of  adjacent  unlike 
minerals  due  to  temperature  changes  of  day  and  night  loosen  the 
crystals,  causing  the  rock  to  crumble.  This  plays  a  more  prominent 
part  in  the  breaking  down  of  coarse-  than  fine-grained  rocks.  In  this 
way  rocks  are  weakened  and  finally  reduced  to  soil  material  by 
other  agencies. 

(b)  Freezing  and  Thawing. — When  water  passes  frorn  the 


FIG.  7. — Columbia  Glacier  overriding  a  forest,  Alaska.     (Courtesy  National  Geographic 
Magazine,  Washington,  D.  C.     Copyright.) 

liquid  to  the  solid  condition  its  volume  is  increased  by  about  nine 
per  cent,  and  the  force  exerted  is  150  tons  per  square  foot,  or  over  a 
ton  per  square  inch.  Water  frequently  freezes  under  conditions  such 
that  part  of  this  force  is  used  in  enlarging  crevices  in  rocks,  break- 
ing off  small  fragments  or  displacing  masses  to  such  an  extents  that 
when  thawing  occurs  they  may  roll  down  the  slope.  This  is  espe- 
cially noticeable  during  a  morning  thaw  on  stony  slopes  free  from 


WEATHERING 


15 


vegetation.  Very  porous  rocks  are  frequently  disintegrated  rapidly 
by  freezing,  especially  when  the  rocks  approach  saturation.  Kocks 
possessing  vertical  joints  or  made  up  of  inclined  strata  of  different 
material  will  weather  rapidly  because  of  greater  absorption  of  water. 
This  action  does  not  occur  in  tropical  or  subtropical  climates,  but  in 
temperate  regions  it  is  very  important  in  breaking  down  rocks  and 
in  keeping  the  subsoil  open  so  that  both  air  and  water  may  enter  the 
soil  much  more  readily  and  carry  on  their  work  to  a  greater  extent 
upon  the  underlying  rocks. 


Fio.  8. — Front  of  Columbia  Glacier  in  1910  compared  in  height  to  Bunker  Hill  Monument. 
The  pinnacle  fell  a  few  minutes  after  the  picture  was  taken.      (Lawrence  Martin.) 

(c)  Glaciers. — At  the  present  time  the  work  of  glaciers  is  lim- 
ited to  a  comparatively  small  area  of  the  earth's  surface  (Figs.  7 
and  8).  During  the  glacial  period  about  half  of  North  America 
and  Europe  were  covered  with  an  ice  sheet,  and  the  work  of  this 
agent  was  very  important  in  that  it  leveled  hills  and  filled  valleys, 
ground  up  and  deposited  large  amounts  of  fine  soil-forming  mate- 
rial. This  deposit  is  found  not  only  on  the  glaciated  areas,  but  was 
carried  far  beyond  the  ice  sheet  by  water  and  further  distributed  by 
the  wind.  (Jlacial  areas  are  now  confined  to  polar  and  a  few  moun- 
tainous regions.  (Jreenland  with  an  area  of  500,000  square  miles  is 


16 


SOIL  PHYSICS  AND  MANAGEMENT 


almost  entirely  covered  by  an  ice  sheet.  This  approaches  somewhat 
the  condition  that  existed  over  North  America  and  Europe  during 
the  glacial  period. 

Glacujrs  are  drainage  systems  of  regions  of  perpetual  snow.  The 
moving  ice  obeys  the  same  laws  as  streams  and  does  the  same  kind 
of  work,  but  the  fact  that  ice  is  a  solid  body  gives  it  great  grinding 
power.  Ice  exerts  a  pressure  Of  forty  pounds  per  square  inch  for 
•every  one  hundred  feet  in  thickness,  and  geologists  estimate  the  ice 
to  have  been  from  a  few  hundred  to  five  thousand  feet  or  more  in 
thickness  during  the  glacial  period.  This  great  pressure  gives  the 
ice  immense  denuding  and  grinding  power.  Glaciers  move  from  a 
few  feet  to  one  hundred  feet  per  day,  the  movement  being  more  rapid 


Fio.  9. — The  material  carried  and  rolled  by  streams  gives  them  their  great  eroding  power. 
(U.  S.  Reclamation  Service.) 

in  summer.  In  their  movement  large  masses  of  rock  become  im- 
bedded in  the  bottom  of  the  glaciers,  grooving  and  grinding  the 
solid  rock  over  which  they  pass.  It  must  be  remembered,  however, 
that  the  ice  did  not  hold  these  rigidly. 

(d)  Erosion  of  Streams. — Flowing  water  doubtless  is  the  most 
extensive  physical  agent  in  the  formation  of  soil  material  at  the 
present  time.  The  streams  with  their  load  of  clay,  silt,  sand,  gravel, 
and  even  boulders  are  not  only  using  these  tools  to  deepen  and  widen 
their  valleys  but  they  also  grind  the  materials  into  powder  fitted  for 
soil  formation.  The  work  of  moving  water  varies  tus  the  square  of 
the  velocity.  If  the  velocity  is  doubled  the  work  that  the  stream  is 
capable  of  doing  will  be  increased  four  times,  since  by  doubling  the 
velocity,  twice  the  number  of  particles  will  strike  an  object  with 
double  the  force.  The  deepening  and  widening  of  the  stream  chan- 


WEATHERING 


17 


nel  is  due  mainly  to  the  mechanical  wear  or  friction  of  the  material 
carried  by  the  water  (Fig.  '.))•  Clear  water  abrades  very  slowly. 
A  rapidly  flowing  stream  carrying  large  amounts  of  material  abrades 
its  bed  very  rapidly.  This  may  be  illustrated  in  the  valleys  that 
have  been  cut  by  streams  that  contain  water  only  after  very  heavy 
rains.  Level  plateaus  have  been  dissected  and  changed  into  a  rugged 
country  of  hills  and  valleys  by  comparatively  small  wet  weather 
streams.  The  entire  land  surface  has  been  greatly  modified  by  this 
process  and  the  transported  material  used  largely  in  soil  formation. 


Fio.   10. — Inner  gorge  of  Grand  Oaflon  of  tho  Colorado  Hivor,  Arizona.     (Walrott,  I'.  S. 

Cionl.  Survey.) 

Captain  C.  E.  Dutton  2  estimates  that  10.000  IVct  of  rock  strata 
have  been  removed  from  an  area  of  LS.OOO  to  15,000  square  miles 
by  the  Colorado  River  (Fig.  10). 

When  quart/  is  ground  up  through  the  action  of  moving  water 
much  sand  is  produced,  and  after  these  particles  have  been  reduced 
to  a  certain  size  the  permanent  water  film  protects  them  largelv  from 
further  attrition.  On  the  other  hand,  feldspars  when  subjected  to 
attrition  form  an  impalpable  mud  or  clay  accompanied  by  consider- 
able loss  of  bases  such  as  potassium,  sodium,  or  calcium,  according 
to  the  kind  of  feldspar. 
2 


18 


SOIL  PHYSICS  AND  MANAGEMENT 


(e)  Waves. — Wave  action  is  confined  to  the  shores  of  seas  and 
the  larger  lakes.  In  many  places  this  agency  breaks  down  solid  cliffs 
into  masses  of  rock  that  become  broken  and  worn  into  rounded 
boulders,  then  to  }>ebl)les,  and  finally  into  fine  material  that  is  car- 
ried away  and  deposited  in  deeper  water  or  in  sheltered  inlets  to 
form  bars.  On  the  Atlantic  coast  of  Britain  waves  sometimes  exert 
a  pressure  of  three  tons  per  square  foot.  The  average  force  is  Gil 
pounds  per  square  foot  in  summer  and  208(>  pounds  in  winter. 
Each  wave  results  in  the  movement  of  more  or  less  material,  and 


Fro.   11. — Wind-carved  granite.     The  tools  were  grains  of  sand.     Camps  Bay,  S.  Africa. 
(Chamberlain  and  Salisbury,  Courtesy  Henry  Holt  &  Co.) 

this  movement  is  accompanied  by  attrition  producing  fine  material. 
Shaler  has  observed  that  at  Cape  Ann,  Mass.,  granitic  paving  blocks, 
weighing  about  twenty  pounds,  when,  exposed  to  the  action  of  the 
surf  for  a  year,  were  worn  into  spheroidal  boulders  that  would  indi- 
cate a  loss  of  more  than  an  inch. 

(f )  Wind. — The  movement  of  wind  is  universal,  but  its  effect 
is  destroyed  or  greatly  reduced,  at  least,  at  certain  seasons  of  the 
year  over  large  areas  of  the  land  surface  by  the  covering  of  vegeta- 
tion. Along  the  coasts,  in  the  arid  interiors  of  continents,  and 
during  winter  and  spring  in  many  areas,  a  large  amount  of  work  is 


WEATHERING 


19 


done  by  the  wind  in  wearing  down  solid  rocks  and  coarse  soil  mate- 
rials into  dust.  The  impact  of  sand  particles  against  rocks  and 
against  each  other  gradually  wears  them  down  into  fine  materials 
(  Fig.  11).  The  largest  number  of  particles  are  moved  near  the  sur- 
face of  the  ground,  hence  the  greatest  amount  of  abrasion  will  take 
place  there.  A  boulder  will  be  worn  away  slowly  on  the  windward 
side  at  the  base  until  it  topples  over,  and  the  process  will  then  l>e 
repeated  until  it  is  entirely  destroyed.  Along  shores  the  glass  in 
windows  of  houses  is  sometimes  worn  through  by  the  impact  of 
sand  particles,  and  an  instance  is 
given  by  Merrill3  where  the  glass  in 
a  lighthouse  was  ruined  during  a  sin- 
gle storm.  Sand  blasts  are  used  to 
produce  ground  glass.  The  natural 
monuments  and  "  mushroom  "  rocks 
in  the  West  owe  their  origin  largely 
to  the  work  of  the  wind. 

(g)  Plants.  —  The  mechanical 
action  of  plants  is  shown  by  the 
growth  of  roots  in  crevices  or  fissures 
of  rocks  and  the  prying  apart  of  great 
masses,  thus  giving  other  agencies 
an  opportunity  for  effective  work. 
The  force  exerted  by  mushrooms  or 
toadstools  is  sometimes  sufficient  to 
raise  blocks  of  stone,  while  cement 
walks  are  frequently  ruined  by  the 
lifting  action  of  roots  of  trees  grow- 

*.  .  ,...•         ,  4 

lllg   adjacent    (I'lg.    12).         Hllgard* 
i          ii   •  i     <t    *     i        i 

makes  this  statement,  Actual  meas- 
urement has  shown  the  force  with  which  the  root.  e.g..  of  the  garden 
pea  penetrates,  to  be  equal  to  from  seven  to  ten  atmospheres  per 
square  inch." 

II.    CIIKMICAI,   ACKNC1KS. 

(a)  Acids.  —  The  atmosphere  in  all  localities  contains  more  or 
less  acid  gases,  which  in  combination  with  the  moisture  of  the  air 
form  acids  that  are  brought  down  with  the  rain.  These  acids  are 
much  more  abundant  in  the  vicinity  of  manufacturing  plants,  smel- 
ters. and  large  cities  where  they  are  produced,  largely  by  the  burning 
of  coal.  Sulfuric  acid  is  probably  the  most  common  of  these  and 


Fio.   12.—  The  roota  of    trw 
wedges  for  prying  rocks  apart. 

l)orl,   U.  S.  Geol.  Survey.) 


20  SOIL  PHYSICS  AND  MANAGEMENT 

contributes  much  toward  the  breaking  down  of  rocks.  Nitric  icid  is 
formed  under  certain  conditions  in  the  atmosphere,  and,  although 
the  amount  reaching  the  surface  of  the  earth  per  acre  per  annum  is 
small,  amounting  at  Rothamsted,  England,  to  from  2.81  pounds  to 
2.98  pounds,  yet  the  long-continued  action  of  this  acid  during  geo- 
logical time  has  done  a  great  deal  toward  breaking  down  rocks  into 
soil  material.  In  some  localities  hydrochloric  acid  forms  a  very 
active  agent,  especially  upon  limestone  and  marble. 

(b)  Carbon  Dioxide. — The  most  effective  acid  in  decomposing 
rocks  is  that  produced  by  the  union  of  carbon  dioxide  and  water,  or 
carbonic  acid.     Carbon  dioxide  is  found  in  the  atmosphere  in  all 
localities,  but,  of  course,  in  slightly  greater  quantities  near  cities 
and  factories  than  at  other  places.    It  is  considered  a  weak  acid,  yet 
because  of  the  fact  that  it  is  always  present,  it  exerts  an  immense 
influence  in  breaking  down  rocks,  especially  those  containing  lime, 
magnesia,  potash,  and  soda.     The  soil  air  contains  much  larger 
amounts  of  carbon  dioxide  than  the  air  above,  thus  percolating  water 
becomes  highly  charged  before  coming  in  contact  with  the  rocks 
beneath.     Carbonated  water  is  an  almost  universal  solvent.     The 
amount  of  carbon  dioxide  in  air  under  different  conditions  is  shown 
by  the  following  table: 

Amount  of  Carbon  Dioxide  in  the  Moil  Air,  and  in  the  Atmosphere' 

Parts  per  million  by  weight 

Ordinary  atmosphere    28i5  to  (500 

Air  from  sandy  subsoil  of  forest 3,800 

Air  from  loamy  subsoil  of  forest 12,400 

Air  from  surface  soil  of  forest 13,000 

Air  from  surface  soil  of  vineyard 14,000 

Air  from  pasture  soil •.  .  .  .          27,000 

Air  fom  soil  rich  in  humus 54,300 

Fischer  lias  shown  that  in  rain  and  snow  water  the  amount  of 
carlxm  dioxide  varies  between  0.22  and  0.4'5  per  cent  by  volume  of 
water.  These  figures  according  to  Merrill  would  give  for  the  Atlan- 
tic Coast  States  a  depth  of  3.75  mm.  of  carbon  dioxide  brought  to 
the  surface  in  rain  and  snow,  for  the  upper  Mississippi  valley  2.50 
mm.,  for  the  lower  Mississippi  valley  4.50  mm.,  and  for  the  North- 
ern Pacific  States  6.25  mm.  Water  percolating  through  soil  would 
absorb  additional  amounts. 

(c)  Oxidation. — The  only  element  that  free  oxygen  of  the  air 
acts  upon  is  iron  when  in  the  sulfide  or  ferrous  condition.     When 
the  iron  of  the  sulfide  is  oxidized,  iron  sulfate  is  formed,  which  is 


WEATHERING  21 

soon  further  oxidized  so  that  the  hydrated  ferric  oxide  and  sulfuric 
acid  are  produced.  The  resulting  oxide  is  much  softer,  more  easily 
removed  by  water  and  more  bulky  than  the  sulfide,  hence  becomes 
quite  absorl>ent  of  moisture  and  is  then  readily  affected  by  freezing 
and  thawing.  The  expansion  produced  by  the  change  tends  to 
loosen  the  crystals  of  the  rock  and  make  it  very  susceptible  to  other 
agencies.  The  same  is  true  in  the  case  of  iron  existing  in  the  ferrous 
condition  either  as  a  carbonate  or  silicate.  The  resulting  products 
of  decomposition  tend  to  color  the  soil  material,  producing  a  yel- 
lowish, brownish,  or  reddish  color. 

(d)  Deoxidation. — Under  certain   conditions  oxygen  will  be 
removed  from  some  compounds,  but  as  a  means  for  breaking  down 
rocks  this  is  not  very  important.     The  chief  agency  in  deoxidatiou 
is  organic  acids.    The  great  afl'mity  of  these  acids  for  oxygen  enables 
them  to  take  part  or  all  of  it  from  certain  compounds,  especially 
those  of  iron,  as  oxides  or  sulfates  producing  a  different  mineral 
with  entirely  different  physical  properties,  the  m,ost  noticeable  of 
which  are  color  and  hardness.    In  swamps  organic,  acids  frequently 
reduce  ferric  oxides  to  ferrous  oxides  and  sulfates  to  sul fides,  result- 
ing in  a  grayish  or  drab  color  in  the  subsoil.     The  gray  subsurface 
and  subsoil  of  many  of  our  poorly  drained  soils  are  undoubtedly 
due  to  the  process  of  deoxidation.     The  soil  under  a  peat  bed  is 
usually  drab,  indicating  a  reduction  of  iron. 

(e)  Hydration. — During  the  process  of  weathering  certain  of 
the  common  minerals  that  compose  igneous  and  metamorphic  rocks 
unite  with  water  which  not  only  changes  the  chemical  composition, 
but  produces  very  important  changes  in  the  physical  character  of  the 
minerals  that  aid  greatly  in  breaking  them  down  into  soil  material. 
This  change  is  usually  attended  with  more  or  less  loss  by  solution. 
One  of  the  most  important  changes  is  ihc  increase  in  volume,  by 
which  there  is  a  tendency  to  rupture  the  rock.    If  no  loss  took  place 
by  solution,  the  change  of  granite  into  soil  through  various  processes 
of  weathering  would  give  an  increase  in  bulk  of  as  much  as  SS  per 
cent,0  a  large  part  of  which  is  due  to  hydration.     At  the  same  time 
the  hardness  of  the  rock  is  lowered  very  materially,  and  this,  of 
course,  gives  other  agencies  a  better  chance.     The  absorption  of 
water  will  also  be  increased  and  free/ing  and  thawing  will  Ix1  more 
effective.    The  general  result  of  hydration  is  to  render  the  rock  very 
susceptible  to  other  agencies.     The  process  of  hydration  goes  on  to 
great  depth.    Apparently  solid  but  hydrated  rock  taken  from  many 


22 


SOIL  PHYSICS  AND  MANAGEMENT 


feet  beneath  the  surface  will  crumble  or  "  slake  "  upon  exposure 
to  the  air. 

(f)  Solution. — Water  is  a  universal  solvent,  but  its  power  is 
greatly  increased  by  the  presence  of  substances  in  solution  so  that 
it  becomes  a  very  active  agent  in  breaking  down  rocks.  Its  efficiency 
is  greatly  increased  by  the  presence  of  carbon  dioxide  which  is 
absorbed  by  rain  water  from  the  atmosphere  and  still  more  from 
the  soil  air  as  it  percolates  through  the  soil,  the  air  of  which  con- 
tains large  amounts  of  carbon  dioxide.  The  water  thus  becomes  a 
very  active  solvent  (see  table,  page  20). 

Effect  of  Decomposition  on  Loss  of  Constituents  from  Rocks  B 


Biotite  granite, 
Georgia 

Syenite, 
Arkansas 

Diabase, 
Virginia 

Diorite, 
Virginia 

Limestone, 
Arkansas 

Fresh 
35  feet 
below 
surface 

Decom- 
posed 
5)4  feet 
below 
surface 

Fresh 

Decom- 
posed 

Fresh 

Decom- 
posed 

Fresh 

Decom- 
posed 

Fresh 

Resid- 
ual 
clay 

SiO2.  .  . 
AM),.  .  . 
Fe2O,..  . 

FeO.  .  . 
CaO... 
MgO.. 
NajO.  .  . 
K20.  .  .  . 
P2O5  .  . 

69.88 
16.42 

\  1.96 

1.78 
0.36 
4.46 
5.63 

51.29 
29.69 

6.33 

0.07 
0.14 
1.12 
1.50 

59.70 

18.85 
4.85 

46.27 
38.57 
1.36 

45.73 
13.48 

37.09 
13.19 

46.75 

17.61 
16.79 

42.44 
25.51 
19.20 

4.13 
4.19 

2.35 
MnO 
4.33 
44.79 
0.30 
0.16 
0.35 
3.04 
34.10 

33.69 
30.30 
1.99 

14.98 
3.91 
0.26 
0.61 
0.96 
2.54 
0.00 

11.60 
9.92 
15.40 
3.24 
.47 

35.69 
0.41 
0.57 
1.75 
0.33 

1.34 
0.68 
6.29 
5.97 

0.34 
0.25 
0.37 
0.23 

9.46 
5.12 
2.56 
0.55 
0.25 

0.37 
0.21 
0.56 
0.49 
0.29 

CO?     .  . 

Ignition 
H2O 

0.36 

10.36 

1.88 

13.61 

0.92 

10.92 

0.94 

11.83 

2.26 

10.76 

Total..  . 

100.85 

100.50 

99.56 

101.00 

100.78 

100.86 

100.01 

99.96 

100.00 

100.00 

In  1848  Rogers  Brothers  7  carried  on.  some  experiments  to  show 
the  power  of  carbonated  water  in  dissolving  minerals  of  different 
kinds.  The  minerals  were  powdered  and  digested  for  48  hours  in 
carbonated  water,  and  from  0.4  to  1  per  cent  of  the  whole  mass  was 
dissolved.  When  40  grains  of  powdered  hornblende  were  digested 
for  48  hours  in  carbonated  water  at  a  temperature  of  GO  degrees  F., 
the  following  peicentages  were  dissolved:  Silica,  0.08;  oxide  of 
iron,  0.095 ;  lime,  0.13 ;  and  magnesia,  0.095.  It  is  to  be  under- 
stood that  this  process  will  not  take  place  so  rapidly  under  natural 
conditions  because  the  minerals  are  more  massive,  but  at  the  same 
time  the  process  is  going  on  constantly.  Richard  Miiller  has  shown 
that  during  seven  weeks  of  treatment  of  minerals  with  carbonated 


WEATHERING 


23 


water  that  0.533  per  cent  of  the  entire  weight  of  oligoclase,  1.530 
per  cent  of  hornblende,  0.307  per  cent  of  magnetite,  2.018  per  cent 
of  apatite,  2.111  per  cent  of  olivine  and  1.211  per  cent  of  serpen- 
tine were  dissolved.  The  calcium,  magnesium,  and  other  alkalis 
were  in  solution  in  the  form  of  carhonates.  Carbonated  water  acts 
very  readily  upon  limestone,  and  the  caverns  found  in  our  large 
limestone  deposits  in  Illinois,  Indiana,  Kentucky,  and  Virginia  bear 


Fio.  13. — Stalactites  and  stalagmites  formed  in  a  cavern  from  limestone  dissolved  by 
carbonated  water  while!  passing  through  the  rocks  above.  Hocks,  Hock-Weathering 
and  Soils,  Merrill.  (Courtesy  The  Macmillan  Company.) 

evidence  of  the  great  solvent  power  of  water.  Tt  is  stated  that  there 
are  150,000  miles  of  subterranean  passageways  in  the  limestone 
region  of  Kentucky,  and  practically  all  of  this  material  was  removed 
by  carlx>nated  water.  In  these  caves  the  stalactites  and  stalagmites 
owe  their  origin  to  the  limestone  dissolved  by  the  water  l>ofore  it 
enters  the  cavern  (Fig.  13).  The  solution  of  the  limestone  has 
produced  sinkholes  on  the  surface  that  gives  a  peculiar  topography 


24 


SOIL  PHYSICS  AND  MANAGEMENT 


to  cave  regions.  These  sinkholes  or  basins  vary  in  size  from  ten  to 
two  hundred  feet  or  more  across  and  from  three  to  fifty  feet  in 
depth  (Fig.  14).  They  vary  in  frequency  as  well  as  size.  In  some 
localities  there  are  only  a  few  small  ones  that  are  not  objectionable, 


Fia.   14. — Sinkholes  in  a  cave  region — Southern  Illinois.     The  bottoms  of  the  sinkholes  are 
still  occupied  by  brush.     (H.  C.  Wheeler.) 

while  in  other  regions  they  are  so  large  and  frequent  that  the  land 
is  entirely  worthless  for  cultivation.  When  the  outlet  from  these  to 
the  cave  becomes  clogged,  "sinkhole  ponds"  result  (Fig.  15).  In 

.  '    .       ' 


Fio.  15. — The    outlets   of   sinkholes    sometimes   become   clogged   and    "sinkhole"    ponds 
result.     (H.  C.  Wheeler.) 


WEATHERING  25 

Hardin  County,  Illinois,  a  lake  varying  in  size  from  100  to  400 
acres  was  produced  by  the  stopping  of  ttie  sinkhole  outlets. 

The  process  of  solution  forms  soil  material  by  the  removal  of 
soluble  substances,  as  in  the  case  of  limestone,  leaving  the  impuri- 
ties, or  as  in  sandstone,  by  taking  out  the  cementing  material,  leav- 
ing the  incoherent  sand,  and  in  the  case  of  igneous  rocks  removing 
some  of  the  potash,  soda,  lime,  magnesia,  or  some  other  compounds, 
and  leaving  a  residue  more  or  less  modified  as  soil-forming  material. 

From  the  amount  of  lime  carbonate  carried  by  the  Thames  River 
it  has  been  estimated  that  the  average  amount  of  this  material  dis- 
solved from  the  limestone  area  drained  by  this  stream  is  1-43  tons 
per  square  mile  in  one  year.9  It  is  estimated  that  on  the  average 
something  like  one-third  as  much  matter  is  carried  to  the  sea 
in  solution  as  in  the  form  of  sediment,  and  that  by  this 
process  alone  land  areas  would  be  lowered  something  like  one 
foot  in  13,000  years.10 

(g)  Plants. — The  roots  secrete  acids  that  attack  the  rocks  and 
aid  solution.  The  roots  of  a  plant  growing  on  a  polished  marble 
surface  removed  the  polish  by  acid  from  the  roots  showing  the  action 
of  the  acids  on  the  rock.  While  this  action  in  the  case  of  a  single 
root  is  very  slight,  yet  it  plays  a  rather  important  part  in  aiding 
decomposition  because  of  the  infinite  number  of  roots  coming  in 
contact  with  the  soil  particles, and  their  long-continued  action. 
This  may  be  shown  where  the  surface^of  stones  are  covered  with 
lichens.  Enough  rock  is  broken  down  to  give  higher  plants,  such  -is 
ferns,  a  chance  to  grow,  and  these  in  turn  by  the  action  of  their  roots 
and  other  agencies  produce  more  soil  material  that  encourages  still 
higher  plants  to  grow.  These  plants  hold  the  material  in  place  and 
allow  sufficient  accumulation  to  form  soils.  The  action  of  the  roots 
of  plants  on  the  minerals  in  soils  is  very  important  while  they  are 
alive,  and  even  when  they  decay  they  aid  materially  in  the  solution 
and  liberation  of  plant  food  and* decomposition  of  rocks. 

(h)  Animals. — Many  animals  burrow  in  the  soil,  and  their 
action  on  the  minerals  tends  to  aid  decomposition  and  disintegration. 
This  is  especially  important  in  the  case  of  earthworms,  ants,  and 
similar  animals.  Many  of  these  carry  vegetable  matter  into  the  soil, 
which,  by  its  decomposition,  aids  in  the  breaking  down  of  minerals. 
Earthworms  pass  large  quantities  of  soil  through  their  bodies, 
the  minerals  of  which  are  acted  upon  by  the  acids  in  the  alimentary 
canal  ami  partly  decomposed.  Kven  the  larger  rodents,  such  as 
gophers,  ground  squirrels,  and  mice  exert  considerable  influence  in 


26  SOIL  PHYSICS  AND  MANAGEMENT 

the  formation  of  soils,  both  in  the  breaking  down  of  minerals  and  in 
mixing  of  soil  and  subsoil. 

QUESTIONS 

1.  Define  weathering. 

2.  Distinguish  between  the  two  forms. 

3.  Does  kaolin  change  into  other  minerals?     Why? 

4.  In  what  ways  do  heat  and  cold  disintegrate  rocks? 

5.  Why  does  not  a  single  hard  freeze  break  all  frozen  rocks  into  fragments? 

6.  Give  the  principal  glacial  areas  of  the  present  time. 

7.  What  is  the  law  for  the  work  of  streams? 

8.  Give  some  good  local  example  of  erosion. 

9.  How  do  the  waves  do  their  work? 

10.  Why  is  the  wind  such  an  effective  erosive  agent? 

11.  What  is  the  source  of  each  of  the  acids  that  aid  in  weathering? 

12.  Why  does  the  soil  air  contain  more  carbon  dioxide  than  the  atmosphere? 

13.  How  does  oxidation  hasten  the  breaking  down  of  rocks? 

14.  Does  deoxidation  aid  in  mineral  decomposition? 

15.  Bring  in  a  sample  of  feldspar  that  shows  hydration. 

16.  Calculate  the  percentage  of  lime  lost  from  each  rock  given  in  table  on 

page  22. 

17.  Calculate  the  loss  of  magnesia  in  the  same  way. 

18.  How  are  stalactites  and  stalagmites  formed? 

19.  Why  are  limestone  soils  so  frequently  acid? 

REFERENCES 

"American  Journal  of  Science,  volume  xxii,  1832,  p.  136. 

*Dutton,  C.  E.~  Tertiary  History  of  the  Grand  C'anon  of  the  Colorado. 

•Merrill,  G.  P.,  Rocks,  Rock- Weathering  and  Soils,  1906,  p.  101. 

*Hilgard,  E.  W.,  Soils,  1906,  p.  19. 

•Johnson,  How  Crops  Feed,  1910,  p.  139. 

•Merrill,  G.  P..  Rocks,  Rock-Weathering  and  Soils,  1906,  p.  166. 

7  American  Journal  of  Science,  volume  v,  1848. 

•Merrill,  G.  P.,  Rocks,   Rock-Weathering  and   Soils,   1906    (Adapted),   pp. 

195-202. 

•  Prestwich,  Quarterly  Journal  Geological  Society,  volume  xxii,  p.  47. 
"Reade,  Liverpool  Geological  Society,  1876  and  1884. 


CHAPTER  III 

THE  PLACING  OF  SOIL  MATERIAL 

I.  RESIDUAL,  GRAVITY-LAID  AND  WATER-LAID  DEPOSITS 

THE  mineral  part  of  soils  is  derived  from  rocks  through  the  work 
of  the  geological  forces  given.  Only  a  small  part  of  the  disinte- 
grated and  decomposed  rock  material  produces  soil  where  first 
formed.  By  far  the  larger  portion  is  moved  from  the  place  of  its 
origin  a  few  feet,  or  it  may  he  thousands  of  miles.  The  mate- 
rial remaining  in  place  produces  sedentary  soils. 

I.    SEDENTARY  FORMATIONS 

Sedentary  Formations  are  those  in  which  the  greater  part  of 
the  material  was  formed  in  place,  as  when  rocks  weather  into 
debris  fitted  for  the  formation  of  soils,  or  when  large  amounts  of 
organic  matter  accumulate  through  the  growth  and  partial  decay 
of  mosses,  grasses,  sedges,  and  other  plants.  This  class  of  forma- 
tions is  divided  into  residual  and  cumulose  soils. 

1.  Residual    Soils. — A    residual    soil    is    one    formed    in    situ 
through   the   decomposition   and   disintegration   of   rocks   and    the 
action  of  organic  agencies.    It  varies  in  composition  with  the  rocks 
from  which  it  is  derived,  and  we  have  in  general  those  materials  (a) 
from   igneous  rocks,   as  granites,   syenites,   diorites,   diabases   and 
others;    (b)    from  aqueous  rocks,   such   as  sandstones,  limestones, 
shales;  and  (c)  from  metamorphic  rocks,  as  gneisses,  schists,  mar- 
bles, and  slates.     By  subsequent  changes  quite  different  soils  result 
even  from  the  same  kind  of  rocks.  The  impression  often  prevails  that 
most  soils  are  residual.    This,  however,  is  not  the  case.     Not  over  two 
per  cent  of  the  soils  surveyed  in  the  I'liitcd  States  by  the  Bureau  of 
Soils'  are  derived  from  igneous  and  metamorphic  rocks,  and  not  over 
five  per  cent  from  sedimentary  rocks  such  as  sandstones  and  shales. 

2.  Cumulose  Soils. — Cumulose  soils  are  formed  by  the  accumu- 
lation of  organic  matter  in  undraincd  areas  to  such  an'  extent  that 
it  forms  a  very  large  portion  of  the  soil.     These  are  divided   into 
swamps  and  marshes,     tf irn.m ftx  are  fresh  water  formations,  while 
the  marches  are  formed  in  brackish  or  salt  water  areas.    The  organic 
matter  of  those  cumulose  deposits  is  derived  chiellv  from  mosses, 
sedges,  and  grasses,  but  almost  any  form  of  vegetation  may  add  to 
the  deposit.     In  north  temperate  and  subarctic  regions  sphagnum 

27 


28 


SOIL  PHYSICS  AND  MANAGEMENT 


moss  gives  rise  to  immense. deposits  of  peat,  in  some  cases  probably 
hundreds  of  feet  in  thickness.  Grasses  usually  grow  with  the 
mosses  and  add  to  the  accumulation.  In  more  southern  regions, 
grasses,  cattails  and  sedges  form'  a  large  part  of  the  deposit,  while 
in  subtropical  regions  the  palmetto  and  saw  grass  constitute  the 
chief  plants  from  which  the  organic  matter  is  derived. 

Swamps  may  be  divided  into  river  swamps,  peat  bogs,  lake 
swamps,  quaking  bogs,  climbing  bogs,  wet  woods  and  ablation 
swamps.  These  terms  are  almost  self-explanatory.  River  swamps 
may  occur  in  the  flood  plain  where  ox-bow  lakes,  representing 


Fio.   16. — Ox-bow  lakes  formed  by   shifting   of  channel,  A,  B  and  C.    Sedimentation   on 
inner  side  of  curve.     (Shaler,) 

former  channels,  have  been  transformed  into  swamps  by  filling  with 
both  organic  matter  arid  sediment  (Fig.  16).  In  wide  flood  plains 
low  swampy  land  may  lie  back  toward  the  bluffs  away  from  the 
river.  Delta  lands  are  usually  swampy. 

Peat  deposits  may  be  formed  (1)  in  low  places  where  the  water 
is  shallow  but  the  supply  constant  (Figs.  17  and  18).  This  type 
is  found  in  sand  dune  or  gravelly  areas  where  the  water  seeps  out 
at  the  base  of  sand  hills  or  gravel  terraces.  Peat  formed  in  this 
way  is  rarely  of  any  great  depth.  Peat  bogs  may  also  be  formed 
(2)  as  shown  in  figure  19.  The  sphagnum  moss  begins  to  grow  at 
the  margins  of  the  lake  and  extends  out  over  the  water,  forming  a 
quaking  bog,  and  up  the  bank,  as  a  climbing  bog.  The  growth  over 
the  water  is  quite  rapid  and  the  small  pond  or  lake  may  become 


RESIDUAL,   GRAVITY-LAID,  WATER-LAID  DEPOSITS        29 

covered  with  a  floating  ma^s  of  vegetation  which  soon  becomes  suf- 
ficiently solid  to  form  a  support  for  other  plants  such  as  rushes, 
graces,  and  sedges.  The  growth  of  these  soon  so  strengthen  this 
floating  mass  that  still  other  species  of  swamp  vegetation,  including 


-&* 


Fia.  17. — Typical  eastern  swamp  land.  The  grass  will  be  preserved  from  decay  in 
the  water.  Leaves  from  the  forest  will  add  to  accumulation.  A  soil  rich  in  organic  matter 
will  result. 


Fia.   18. — Florida  everglades. 

some  shrubs,  gain  a  foothold.  Forest  trees  may  ultimately  cover 
it.  While  the  process  above  described  is  taking  place  partly  decayed 
vegetation  is  dropping  to  the  bottom  of  the  lake  from  the  under 
side  of  the  floating  mass,  and  this  accumulation  may  go  on  till  £he 


Fia.  19. — Section  showing  one  stop  in  the  filling  of  tholnke  with  poat ;  cc,  moss  growing 
on  surface  of  lake;  dd,  partly  decayed  peat  that,  has  fallen  from  floating  mass;  ee,  climbing 
bog.  (Shaler.) 

pond  or  lake  becomes  completely  filled.  Accumulations  of  peat  also 
occur  around  springs,  giving  rise  to  quaking  bogs  (Fig.  20).  In 
poorly  drained  areas  the  moss  may  grow  on  the  surface  of  the  soil 
in  sufficient  amounts  to  fojrm  peat.  Oftener,  however,  it  forms  only 
a  soil  rich  in  organic  matter. 


30 


SOIL  PHYSICS  AND  MANAGEMENT 


A  wet  woods  swamp  is  where  a  forest  area  with  a  slope  of  less 
than  five  degrees  has  heen  transformed  into  a  swamp  through  the 
accumulation  of  vegetable  material  and  the  consequent  increase  of 
moisture.  The  original  forest  may  be  entirely  destroyed  and  re- 
placed by  plants  adapted  to  swamp  conditions. 

An  ablation  swamp  is  produced  by  the  solution  and  carrying 
away  of  certain  more  soluble  strata,  such  as  gypsum,  salt  or  even 
limestone,  between  less  soluble  strata,  thus  causing  a  lowering  of 
the  surface  and  bringing  about  swamp  conditions. 

II.      TRANSPORTED  FORMATIONS 

Various  agencies  are  engaged  in  the  movement  of  soil  material, 
namely:  gravity,  water,  ice,  and  wind,  and  the  deposits  formed  by 


Fio.  20. — Hummocks  6  to  12  inches  high,  found  in  swampy  places  produced  by  trampling  of 
stock.     Commonly  called   "bogs."     (R.  W.  Dickenson.) 


these  are  known  as  colluvial,  sedimental,  glacial,  and  eolial.  During 
the  transportation  of  these  materials  many  particles  are  reduced 
in  size  and  other  changes  brought  about.  Over  ninety  per  cent  of 
the  soils  surveyed  by  the  Bureau  of  Soils  *  in  the  United  States  are 
formed  from  transported  material. 

1.  Colluvial  or  Gravity-laid  Soils. — Gravity  might  be  said  to 
be  the  active  agent  in  the  formation  of  all  of  the  above,  but  gravity, 
unaided,  is  very  limited  in  its  work,  being  confined  to  areas  of 
vertical  cliffs  or  very  steep  slopes.  The  material  transported  by 
gravity  and  deposited  at  the  base  of  cliffs  consists  of  a  heterogeneous 
mixture  of  detritus  that  has  been  loosened  by  the  processes  of 
weathering  and  carried  downward  by  gravity.  This  accumulation 
is  commonly  designated  as  talus  or  cliff  debris  (Figs.  21  and  22). 


RESIDUAL,  GRAVITY-LAID,  WATER-LAID  DEPOSITS        31 


Fio.21. — Weathering  of  jointed  rork  above  and  thint>r<l 
at  base.  Near  Bluff  City,  Utah.  Rocks,  Roek-WeaUu-rin 
the  Macfliillan  Co.) 


32 


SOIL  PHYSICS  AND  MANAGEMENT 


It  shows  very  little  or  no  assorting  action,  although  in  some  cases 
the  finer  material  may  be  washed  out  by  water  and  deposited  at  the 
base,  thus  leaving  the  coarser  material  higher  up  on  the  slope,  while 


FIG.   22. — Rock  disintegration  and  formation  of  talus  slope.    More  advanced  stage.    Mount 
Sneffels,  Colo.     (Merrill.) 


(From  Elements  of  Geology,  Copyright  1911.  by  Eliot  Blackwelder  and  Marian  II.  Barrows. 
American  Book  Company,  Publishers) 

Fio.  23. — The  side  of  a  ravine  near  Crawfordsvillc,   Indiana.     The  more  rapid  creep  of 
surface  material  has  caused  the  trees  to  lean  down  hill. 

in  other  cases  the  coarser  material  may  roll  down  the  slope  to  a 
greater  distance,  leaving  the  finer  at  the  top.  This  process  of  weatb- 
ering  and  downward  movement  of  material  will  finally  transform 
ihe  vertical  cliff  into  a  steep  slope  which  will  represent  the  angle 


RESIDUAL,  GRAVITY-LAID,  WATER-LAID  DEPOSITS         33 

of  rest  of  the  detritus.  The  downward  movement  does  not  stop  here, 
for  there  is  a  certain  amount  of  "  creep  "  due  to  freezing  and  thaw- 
ing, and  the  action  of  water  aided  by  gravity  (Fig.  23)  that  ulti- 
mately reduces  the  slope  so  that  it  may  be  cultivated.  These  talus 
slopes  are  small  in  extent  and  are  of  very  little  agricultural  value 
because  of  their  stony  character. 

2.  Sedimental  or  Water-laid  Soils. — The  material  forming 
these  deposits  has  been  carried  in  suspension  or  rolled  along  the 
beds  of  streams  for  a  greater  or  less  distance  from  their  place  of 
origin.  When  a  body  is  immersed  in  water,  it  los.es  weight  equal 
to  the  weight  of  the  water  displaced  by  it.  This  buoyant  effect 
enables  fine  particles  to  remain  in  suspension  for  a  long  time  and 
renders  coarser  material  more  easily  moved  than  when  in  the 
atmosphere.  The  total  amount  of  material  carried  by  running 
water  varies  as  the  fifth  2  power  of  its  velocity  while  the  size  of 
particles  carried  varies  as  the  sixth  power,  so  that  doubling  the 
velocity  increases  the  amount  of  material  thirty-two  times  and  the 
size  of  material  carried  sixty-four  times.  If  the  velocity  wero 
trebled  the  amount  is  increased  two  hundred  and  forty-three  and 
the  size  is  increased  seven  hundred  and  twenty-nine  times.  Then 
if  a  given  current  carries  particles  .1  mm.  in  diameter  doubling 
its  velocity  enables  it  to  carry  material  (i.4  mm.  in  diameter,  or 
trebling  the  velocity  enables  it  to  carry  particles  72. !>  mm.  in 
diameter.  The  following  table  shows  the  character  of  material  that 
may  l>e  carried  or 'swept  along  by  the  current. 

The  Material  Carried  by  Water  of  Varied  Velocity* 

Inches  per         Miles  per 
second  hour 

3 0.170  — will  just  move  fine  clay. 

(5 0.240  —will  lift  fine  sand. 

8 0.4545 — will  lift  sand  as  coarse  as  linseed. 

12 0.08 1U — will  sweep  along  line  gravel. 

24 1.3038 — will  roll    rounded    pebbles    1    inch    in   diameter. 

30 2.045  — will  sweep  along  slippery,   angular   stones   the 

size  of  an  egg. 

Another  factor  in  the  transportation  of  soil  material  is  given 
by  King.4  When  a  particle  is  immersed,  it  attracts  a  film  of  water, 
which  becomes  an  essential  part  of  the  particle,  moving  with  it 
wherever  it  goes.  The  specific  gravity  of  soil  particles  is  approxi- 
mately 2.65.  The  immersed  solid-liquid  body  has  such  low  specific 
gravity  that* very  little  force  is  required  to  keep  it  in  suspension 
and  so  it  becomes  possible  for  a  particle  to  bo  carried  hundreds  of 
miles.  This  adherent  film  averages  about  .f>r>  mm.  in  thickness.  T>y 
computation  we  find  that  a  clay  particle  .001  mm.  in  diameter  with 
3 


SOIL  PHYSICS  AND  MANAGEMENT 


RESIDUAL,  GRAVITY-LAID,  WATER-LAID  DEPOSITS          35 


a  film  .01  mm.  thick  has  a  specific  gravity  of  1.0002.  This  is  so  near 
the  specific  gravity  of  water  that  the  particle  will  remain  in  suspen- 
sion indefinitely.  Professor  King  estimates  that  a  force  of  only  4.4 
pounds  is  necessary  to  keep  the  11  tons  of  sediment  in  suspension 
that  is  delivered  at  the  mouth  of  the  Mississippi  Kiver  each  second. 
The  increase  of  the  effective  diameter  of  the  particle  augments  the 
effective  cross-section  441-fold,  and  so  only  a  very  small  vertical 
motion  would  he  required  to  maintain  suspension.  The  effective 
volume  would  he  increased  9,201-fold  by  the  adhering  film.  When 
a  particle  of  dust  is  suspended  in  the  atmosphere  it  attracts  a  film 
of  air  which  moves  with  it  in  the  same  way  as  the  film  of  water  and 
lessens  its  specific  gravity,  thus  enabling  it  to  be  held  in  suspension 
with  a  much  smaller  force  than  would  otherwise  be  necessary.  The 
specific  gravity  of  a  clay  particle  .001  mm.  in  diameter,  with  an 
adherent  film  of  air,  is  1.233G.  For  computing  the  specific  gravity 
of  a  particle  immersed  in  water  the  following  formula  may  be  used: 


Sp.  Gr.= 


?rd3X  sp.gr. 
0~ 


d3X  sp.gr.  + 
D3 


*D» 

6 

irD3 

-  =  volume  of  a  sphere. 
o 

d  =  diameter  of  particle  or  solid  nucleus 

sp.  gr.  =  specific  gravity  of  the  nucleus 

D=- diameter  of  solid-fluid  system 

Sp.  Gr.  =  specific  gravity  cf  the  solid-fluid  system 

The  amount  of  material  carried  by  the  Mississippi  River  and 
deposited  in  the  (Julf  of  Mexico  annually  is  equivalent  to  the  re- 
moval in  (5,000  years  of  a  layer  one  foot  thick  over  the  entire  drain- 
age area. 

Amount  of  Sediment  Carried  in  Suspension  Annually  5 


River 

Drainage 
areas  in 
sq.  mi. 

Mean 
annual 
discharge 
in  cu.  ft. 
per  second 

Total 
tons 
annually 

Ratio  of 
sediment 
to  water 
by  weight 

Height 
in  ft.  of 
column  of 
sediment, 
base 
1  sq.  mi. 

Thickness 
of  sedi- 
ment in 
in.  if  spread 
over   drain- 
age area 

Potomac  .  .  . 
Mississippi  . 
Rio  Grande. 
Uruguay  .  .  . 
Rhone  
Po  

11,013 
1,244,000 
30,000 
150,000 
34,800 
27,100 

20,100 
610,000 
1,700 
150,000 
65,850 
62,200 

5,557,250 
400,250.000 
3,830,000 
14,782,f.<)0 
3C).(M)(),000 
07.000000 

1:    3,575 
1:     1,500 
1:       291 
1:  10,000 
1:     1,775 
1  :        900 

4.0 
241.4 
2.8 
10.6 
31.1 
59.0 

.00433 
.00223 
.00116 
.00085 
.01075 
.01139 

Danube.  .  .  . 
Nile  

320,300 
1  100000 

315,200 
1  13,000 

108.000,000 
"4,000.000 

1  :    2,880 
1  :     2,050 

93.2 

38.8 

.00354 
.00042 

Irrawaddy.. 
Mean  

125,000 
334,693 

475,000 
201,468 

291.430,000 
109,649,972 

1:     1,010 
1:    2,731 

209.0 
76.65 

.02005 
.00614 

36 


SOIL  PHYSICS  AND  MANAGEMENT 


Classes  of  Sedimental  Soils. — There  are  three  classes  of  sedi- 
mental  soils,  marine  or  sea-laid,  lacustrine  or  lake-laid,  and  alluvial 
or  stream-laid. 


Fio.  25. — Map  showing  the  early  stages  in  the  formation  of  coast  marshes.     The  numbers 
indicate  the  depth  of  water  in  fathoms.      (C.  and  G.  Survey.) 

(a)  The  marine  or  sea-laid  deposits  are  formed  along  sea  coasts 
(Fig.  25)  and  include  bars,  spits,  hooks,  and  marshes.  Bars  fre- 
quently produce  lagoons  that  ultimately  become  marshes.  Marine 


Fio.  26. — Section  of  marine  marsh;  6,  grass  marsh;  c,  mud  bank,  or  mud  Sate;  d,  eel-grass. 

(Shaler.) 


RESIDUAL,  GRAVITY-LAID,  WATER-LAID  DEPOSITS         37 

and  salt  marshes  are  divided  into  those  above  mean  tide,  as  the 
grass  marshes  and  mangrove  marshes,  and  those  below  mean  tide, 
mud  banks  and  eel-grass  areas  (Fig.  20).  The  mangrove  marshes 
occur  along  the  Florida  coast  and  have  played  a  very  important 
part  in  adding  to  the  land  area  (Fig.  27).  The  other  form  of 
marshes  occur  in  more  northern  regions,  the  grass  marshes  being 


Fio.  27. — Mangrove  mar8h,  Biscaync,  Florida.  This  mangrove  advances  into  the 
water  by  throwing  out  new  roots.  (From  Elements  of  Geology.  Copyright  1911,  by 
Eliot  Blackwelder  &  Harlan  H.  Barrows.  American  Book  Company,  Publishers.) 

sufficiently  high  so  that  they  are  covered  only  during  the  highest 
tides.  The  eel-grass  banks  are  always  covered,  while  the  mud  bank 
is  intermediate  between  these.  Holland  is  an  illustration  of  what 
the  marsh  lands  may  become,  when  drained  and  protected  by  dikes, 
(b)  Lacustrine. — Lacustrine  or  lake-laid  deposits  consist  of 


Fio.   28. — Tx;vel  floor  of  Lake  Chicago,  with  the  shore-line  in  the  distance.    (R.  W.  Dickenson.) 

(1)  terraces  and  beaches  representing  old  water  levels  and  shores 
and  (2)  the  beds  of  extinct  lakes.  During  glacial  times,  main- 
lakes  were  formed  by  the  obstruction  of  drainage  and  many  more 


442988 


38 


SOIL  PHYSICS  AND  MANAGEMENT 


were  filled  to  a  greater  or  less  height  with  gravel  and  sand.  Lake 
Agassiz,  covering  a  large  area  in  Minnesota,  North  Dakota,  and 
Canada,  represents  the  former,  while  Lake  Chicago  (Fig.  28),  an 
extension  of  Lake  Michigan  to  the  south,  and  Maumee  T.<ake,  an 
enlargement  of  Lake  Erie,  are  examples  of  the  latter  (Fig.  41). 


FIQ.  29. 


•Terraces  of  Frazier  River  at  Lilloet,  B.  C.     Six  in  number.     (Chamberlain  and 
Salisbury,  Courtesy  Henry  Holt  &  Co.) 


All  of  the  Great  Lakes  were  much  more  extensive  then  than  now 
and  subsequent  drainage  lowered  the  water  and  exposed  parts  of  the 
old  bed  which  now  constitute  lacustrine  deposits.  These  give  us 
some  of  our  best  soils.  Loess  and  adobe  may  be  formed,  in  part 
at  least,  in  lakes. 

(c)   Alluvial. — The  alluvial,  or  stream-laid  deposits,  include, 
first,  terraces,  commonly  called  second  bottom  or  bench  lands,  that 


Fio.  30. — Terrace  along  Creek,  near  Rockford.   Illinois,  showing  stratification.      (H.  W. 

Stewart.) 


RESIDUAL,  GRAVITY-LAID,  WATER-LAID  DEPOSITS          39 


represent  the  former  Hood  plains  of  streams  which  now  flow  at  a 
lower  level;  second,  first  bottom  lands,  or  present  flood  plains;  third, 
deltas;  and  fourth,  alluvial  cones  and  fans. 

Terraces  originate  in  three  ways :  ( 1 )  those  formed  hy  depo- 
sition of  material  from  overloaded  streams  giving  rise  to  sand, 
gravel,  or  silt  terraces  (Fig.  29).  These  occur  principally  along 
the  streams  that  carried  the  d-ainage  from  the  melting  glaciers. 

V.'iuMi  the  current  decreased,  the 
load  was  dropped  and  the  valleys 
were  filled  to  a  greater  or  less 
height  with  gravel  and  sand.  In 
some  cases  the  valleys  were  filled 
almost  to  a  level  with  the  upland 
(Figs.  30  and  31).  Farther 
down  the  stream  the  terrace  be- 
came lower  and  the  finer  material 
was  deposited.  When  the  glacier 
retreated,  the  stream,  having  no 
load  to  carry,  would  begin  to  cut 
down  through  the  gravel  and 
soon  this  formation  would  be 
much  above  the  stream  and  con- 
stitute a  terrace,  second  bottom, 
or  bench  land.  The  same  action 
might  take  place  down  the  stream 
where  the  finer  material  was 
deposited.  (2)  Those  formed 
through  deration  of  land  and 
consequent  rejuvenation  of  the 
stream,  thus  causing  it  to  cut 

Fl°'  31'C'°i<'W n flmvn    lnro"-n   nn<1   abandon   the 
r  old  flood  plain  and  form  a  new 

1  hose  formed  by  i>o,,<Knri  of  tributary  stream*  due  to  the 
building  up  of  the  Hood  plain  of  fbe  main  stream  more  rapidly  than 
that  of  the  tributaries.  Tn  this  wnv  the  lower  part  of  the  tributary 
valley  is  formed  into  a  lake  which  would  receive  a  deposit  of  (im- 
material from  the  tributary  but  conrse  from  ihe  inrushing  waters 
from  the  main  stream  during  floods.  A  reduction  of  the  wafer 
supply  and  the  amount  of  sediment  carried  by  the  main  stream 
will  enable  the  tributary  to  cut  down  into  the  flood  plain,  drain  the 
lake,  and  form  a.  new  valley  in  the  fill.  (Jood  examples  of  this  are 


40  SOIL  PHYSICS  AND  MANAGEMENT 

seen  along  the  tributaries  of  the  Mississippi  and  Wabash  Rivers. 
The  very  heavy  soils  along  these  have  been  formed  in  this  way. 

QUESTIONS 

1.  What  are  sedentary  formations? 

2.  Distinguish  between  residual  and  cumulose  soils. 

3.  Give  history  of  an  ox-bow  lake;  its  formation  and  filling. 

4.  Give  four  ways  in  which  lakes  may  become  extinct. 

5.  What  conditions  give  rise  to  peat? 

6.  How  is  peat  formed? 

7.  What  is  a  climbing  bog  and  how  formed? 

8.  How  may  a  wet  woods  become  a  swamp  ? 

9.  Draw  a  diagram  showing  how  ablation  swamps  may  be  formed. 

10.  How  are  colluvial  soils  formed? 

11.  What  is  meant  by  the  "creep"  of  material  on  hillsides? 

12.  What  are  the  laws  for  the  carrying  power  of  running  water. 

13.  Give  an  example  of  this  power. 

14.  What  is  the  specific  gravity  of  a  soil  particle  .01  mm.  in  diameter  and 

its  inclosing  film  of  water  .05  mm.  thick? 

c,  y^  15.  How  long  would  be  required  for  the  Potomac  River  to  remove  12  inches' 
of  material  from  its  drainage  basin  at  the  rate  given  in  table  p.  35? 

16.  W7hat  are  the  divisions  made  of  marshes? 

17.  What  are  the  forms  of  lacustrine  deposits? 

18.  How  are  terraces  formed? 

REFERENCES 

1  Marbut,  C.  F.,  Bennett,  H.  H.,  Lapham,  J.  E.,  and  Lapham,  M.  H.,  Bulletin 

96,  Bureau  of  Soils,  U.  S.  D.  A.,  1!)13,  p.  10. 
1  Deacon,   G.   F.,   Inst.   Civil    Engineering   Proceedings,    volume    118,    1894, 

p.  93-96. 

*Geikie,  Textbook  of  Geology,  3rd  edition. 
*King,  F.  H.,  Suspension  of  Solids  in  Fluids  and  the  Nature  of  Colloids 

and  Solutions,  Transactions   Wisconsin   Acad.  Sci.,  Arts  and   Letters, 

volume  16,  part  1,  1908. 
•Babb,  Science,  volume  21,  1893,  p.  343. 

General  References. — McGee,  W.  J.,  Bulletin  7'1,  Bureau  of  Soils, 
U.S.D.A.,  1911,  Soil  Erosion.  Davis,  R.  O.  E.,  Bulletin  180,  U.S.D.A.,  1915, 
Soil  Erosion  in  the  South.  Salisbury,  R.  D.,  Agencies  which  Transport 
Material  on  the  Earth's  Surface,  Journal  of  Geology,  volume  iii,  p.  170. 


CHAPTER    IV 


THE   PLACING   OF   SOIL   MATERIAL    (Continued) 
II.   GLACIAL    OR   ICE-LAID    DEPOSITS 

THE  glaciers  and  ice  sheets  of  former  times  covered  extensive 
areas  with  deposits  of  material  that  may  be  divided  into  morainal, 
intermorainal,  drunilins,  kames,  and  eskers.  During  the  glacial 
period,  practically  all  of  North  America  north  of  the  Ohio  and 
Missouri  Rivers,  amounting  to  4,000,000  square  miles,  was  covered 
with  an  ice  sheet  (Fig.  32)  that  had  gradually  pushed  southward 


Fia.    32. — Front  of  Chenega  Glacier  compared  with  Washington  Monument,  550  feet  high. 

(Lawrence  Martin.) 


"•••"  •  ';     7 
.  v    " 

S5fe£._-  •  ;,j 


~* 

.,*    "<*f.-.*'--v'-;! 

Fio.   33. — Very  stony  and   gravelly  phase   of   glacial  drift  near  Whitewater,   Wisconsin 

(King.) 

41 


42  SOIL  PHYSICS  AND  MANAGEMENT 

from  three  centers  of  accumulation  in  Canada.  The  northwestern 
half  of  Europe  was  covered  at  the  same  time.  Vast  quantities  of 
material  of  all  sizes  and  all  kinds  of  rocks  were  transported  and 
deposited  when  the  ice  melted,  leaving  a  mantle  of  boulder  clay, 
drift,  or  till,  varying  from  a  few  inches  to  several  hundred  feet  in 
thickness.  The  average  depth  of  the  deposit  for  Illinois,  according 
to  Leverett,1  is  about  115  feet.  These  glacial  deposits  constitute  the 
material  from  which  the  soils  were  formed  over  a  large  area  east  and 
north  of  Illinois,  but  in  the  middle  west  a  deposit  of  loess  has 
buried  the  drift,  producing  soils  of  an  entirely  different  character 
(Fig.  33).  In  glaciated  Europe  the  same  conditions  exist  in  regard 
to  soils. 


FIG.  34. — Limestone  boulder  showing  glacial  scratches.     Urbana,  111. 

The  drift  left  by  glaciers  is  only  one  of  the  important  things 
accomplished  by  them.  The  enormous  pressure  of  the  ice,  40  pounds 
per  square  inch  for  each  hundred  feet  in  thickness,  enabled  it  to 
wear  down  hills  and  fill  valleys,  especially  if  they  extended  nearly 
at  right  angles  to  the  direction  of  the  movement.  Otherwise  it 
might  deepen  and  broaden  them,  but  on  the  whole  its  effect  has  been 
to  leave  the  country  more  nearly  level  than  before.  Many  regions 
have  been  transformed  from  hilly  areas  of  low  agricultural  value 
to  undulating  or  rolling  lands  well  adapted  to  agriculture.  The  ice 
in  its  movement  southward  picked  up  large  quantities  of  detritus 
of  all  kinds  and  sixes  and  ground  it  into  fine  material  fitted  to  form 
soils.  Much  of  this  material  was  carried  from  400  to  1,000  miles 
or  more  and  during  its  transportation  boulders  (Fig.  34)  and  gravel 
would  rub  and  grind  against  each  other  and  against  the  rock  sur- 


GLACIAL  OR  ICE-LAID  DEPOSITS 


43 


faces  over  which  they  moved  (Fig.  35),  producing  immense  quan- 
tities of  rock  flour.  The  whole  glacier  was  an  immense  mill  that 
was  slowly  grinding  rocks  into  powder.  This  rock  flour  was  lib- 


Fio.   35. — Glacial  grooves  or  stria?  on  rork  surface.     Northern  Ohio.      (From   Elements  of 
Geology,  Copy:  i^ht  1911,  by  Kl.ot  Black  welder  A  llarlanH.  Harrows.  American  Book  Co.) 


Fid.   30. — Typical  topography  of  terminal  moraine  near  Ocomowoo,  Wisconsin.     Wisconsin 
Geol.  Survey.     (Fount-man.) 

erated  by  the  melting  ice  and  was  distributed  over  the  land  by  water 
and  wind,  forming  the  very  best  of  soil  material.  In  some  in- 
stances it  was  carried  much  farther  than  tlu>  limit  of  the  ice  sheet 
and  distributed  as  immense  aprons  beyond  the  ice  front. 


44 


SOIL  PHYSICS  AND  MANAGEMENT 


Fio.  37. — Drumlins — remnants  of  former  terminal  moraines.     (U.  8.  Geol.  Survey.) 


Fia.  38. — Drumlin — transverse  view.  By  Aldcn.     (U.  S.  Geological  Survey.) 


Fio.  39. — Adeline  eaker,  Ogle  County,  Illinois.      Thin  esker  is  over  nine  miles  in  length 

(rl.  W.  Dickeneon.) 


GLACIAL  OR  ICE-LAID  DEPOSITS 


45 


The  material  carried  and  pushed  along  by  the  ice  is  usually  very 
irregularly  distributed,  giving  the  glaciated  areas  an  undulating 
to  rolling  topography.  The  ridge  formed  at  the  terminus  of  the 
glacier  is  the  terminal  moraine  (Fig.  3(>).  It  usually  presents 
a  steep  outward  slope  with  a  very  gradual  inward  slope.  The 
surface  of  the  moraine  is  rolling,  billowy,  or  has  "  rounded  knob  and 
basin"  topography.  The  height  of  moraines  may  vary  from  a  few 
feet  to  several  hundred,  while  the  width  may  be  from  a  half  mile 
to  ten  miles  or  more.  Recessions  and  advances  of  the  glacier  may 
build  up  new  moraines  or  override  old  ones,  tearing  them  down 
completely  or  transforming  the  material  into  lenticular  hills,  called 
drumlinx  (Figs.  37  and  3S),  whose  longer  axis  i<  in  the  direction 
of  movement  of  the  latest  ice  sheet. 

Super-  and  subglacial  streams  formed  hills  of  gravel  and  sand 
called  kam.es,  or  ridges  of  the  same  material  called  eskers  (Figs.  30 
and  40). 


Fia.  40. — The  material  composing  Adeline  csker  consists  of  coarse  sand  and  gravel. 
The  ledge  is  conglomerate  formed  by  cementing  the  mind  and  gravel  with  carbonate  of  lime. 
(R.  W.  Dickenson.) 

The  Glacial  Period. — The  three  centers  of  accumulation  in 
North  America  during  the  glacial  period  were  the  Labradorean  in 
Labrador,  the  Keewatin  immediately  west  of  Hudson  Hay,  and  the 
Cordilleran  in  the  Kooky  Mountains  of  Canada.  These  centers  cov- 
ered large  areas  (Fig.  I',*),  and  ice  movement  started  from  these  in 
practically  all  directions,  but  probably  not  from  all  centers  at  the 
same  time,  or  at  least  not  to  the  same  extent.  Smaller  centers  of  ae- 


46 


SOIL  PHYSICS  AND  MANAGEMENT 


cumulation  existed  in  the  Rocky  and  Sierra  Nevada  Mountains  and 
on  the  Island  of  Newfoundland.  In  Europe  (Fig.  43)  the  Scandina- 
vian was  the  principal  and  the  Ural,  a  secondary  center.  The  glaciers 
of  the  Alps  and  Caucasus  were  much  more  extensive  than  at  present, 
(a)  The  Jerseyan  or  Nebraskan  Glaciation  and  Aftonian 
Interglacial  Stage. — The  first  glacial  advance  probably  came  from 
the  Keewatin  center  and  is  called  the  Jerseyan  or  the  Nebraskan, 
because  small  areas  of  surface  deposits  made  by  this  glacier  are 
found  in  those  states.  All  other  deposits  of  this  advance  have  been 
buried  by  subsequent  ice  sheets  and  it  is  difficult  to  make  a  careful 
study  of  them  because  of  superposed  material.  There  is  no  evidence 
that  the  area  between  New  Jersey  and  Nebraska  was  covered  by 


Fio.  41. — Map  showing  extent  and  southern  limit  of  glaciation  in   North  America. 
Also  Lakes  Agassiz,  Lahonton  and  Bonneville.     (Compiled  from  several  sources.) 

this  ice  sheet.  This  glacier  receded  and  the  drift  deposited  by  it 
became  eroded,  weathered  and  the  surface  was  changed  into  soil. 
Even  peat  beds  were  formed  in  undrained  areas.  This  inter- 
glacial  stage  is  known  as  the  Aftonian. 

(b)  The  Kansan  Glaciation  and  Yarmouth  Interglacial 
Stage. — The  second  glacial  advance  was  from  the  Keewatin  center 
also,  and  extended  into  Iowa,  Illinois,  Nebraska,  and  Kansas,  and 
derived  its  name  from  the  exposure  of  drift  in  the  latter .  state. 
After  the  ice  receded  soil  was  formed  from  the  surface  of  the  drift 


GLACIAL  OR  ICE-LAID  DEPOSITS 


47 


and  organic  matter  accumulated  as  peat  in  some  swampy  areas. 
This  stage  is  known  as  the  Yarmouth. 

(c)   The  Illinoisan  Glaciation  and   Sangamon  Interglacial 
Stage. — The   third    glacial    advance    was    from   the   Labradoreau 


Fio.   42. — Map  .showing  the  three  renters  of  ire  accumulation  in  North   America.     (Cham- 
berlain ami  Salisbury.      Courtesy  Henry  Holt  &  Co.) 

center  and  was  Hie  most  extensive  in  the  middle  west  during  the 
entire  period  of  glaciation.  The  greatest  area  of  surface  deposits  is 
in  Illinois,  hence  the  name.  It  is  exposed  in  Ohio,  and  Indiana,  also. 
This  glaciation  was  followed  by  a  long  interglacial  stage  during 
which  weathering  and  soil  formation  occurred.  It  is  known  as 


48 


SOIL  PHYSICS  AND  MANAGEMENT 


the  Sangamon  stage  (Fig.  44).  Peat  deposits  have  been  found  as 
much  as  22  feet  in  thickness  that  were  formed  during  this  period, 
(d)  lowan  Glaciation,  Loess  Deposits  and  Peorian  Inter- 
glacial  Stage. — The  Sangamon  interglacial  stage  was  followed 
by  the  lowan  advance  from  the  Keewatin  center  and  covered  a  con- 
siderahle  part  of  Minnesota,  Wisconsin,  northeastern  Towa  and  the 
northern  part  of  Illinois.  The  conditions  at  the  time  of  the  melting 
of  this  glacier  gave  rise  to  extensive  loess  deposits. 


During  sum- 


EUROPE 

'"•»lnc  distribution  of  Ice'durlnK  Epoch  o'f  M 
[•lactation,  and  chief  areaa  occupied  bj.snow. 
local  ice-sheets, 'and  glacleri  during 
Fourth  Glacial  Epoch.  / 

I""""]  Eporh  of  Maiitnum  Olaclatloo: 
'          (S«o,,J  UUciil  Epoch) 

I         I  Epoch  of  flreat  Baltic'Giacler: 

1 '     ""    nK  ou.  i.i          - 


Fio.  43. — Map  showing  extent  of  ice-sheet,  Europe.    (Reproduced  from  Dana's  Manual  of 
Geology,  by  special  arrangement  with  American  Book  Company.) 

mer  the  melting  was  very  rapid  so  that  the  flood  plains  of  streams 
draining  from  the  glacier  received  deposits  of  rock  flour  during 
these  periods  of  overflow.  During  times  of  little  melting  the 
streams  contracted  to  their  ordinary  channels,  leaving  the  material 
exposed  on  their  flood  plains.  This  was  picked  up  hy  the  wind  and 
distributed  over  the  upland  where  it  occurs  as  a  deposit  from  3  to 
150  feet  in  thickness  over  part  of  the  states  bordering  the  Mississippi 
and  Missouri  Rivers.  The  loess  buried  the  Sangamon  soil. 

The  Peorian  interglacial  stage  followed  the  lowan  glaciation, 


GLACIAL  OR  ICE-LAID  DEPOSITS 


49 


Fia.  44. — A  section  showing  the  black  Bangamon  soil  with  the  Illinois  glacial  drift 
beneath  and  tho  lowun  loess  above,  with  the  present  soil  on  the  surface.  Knox  County, 
Illinois.  (F.  Leverett,  LI.  S.  Geol.  Survey.) 


Fio.   45.— A   section   showing    fal    nionminRtoi 
loess;  (d)  Sangamon  soil;  (e)  Silt  below  peat. 


urnvrl;  (b)  Shelby villo  till  shoot;  (c)  lowi 
(Dr.  Samuel  Calvin,  U.  S.  Geol.  Survey.) 


50  SOIL  PHYSICS  AND  MANAGEMENT 

during  which  the  surface  loess  was  changed  into  soil  which  was 
later  buried  in  part  by  subsequent  glaciers.  The  soils  and  peat  beds 
of  the  Peorian  stage  contain  remains  of  cedar  trees  which  grew  in 
the  extensive  swamps  that  existed  at  that  time. 

(e)  Early   Wisconsin   Glaciation,   Loess   and    Interglacial 
Stage. — The  Peorian  stage  was  ended  by  another  ice  advance  known 
as  the  Early  Wisconsin   (Fig.  45),  which  came  from  the  Labra- 
dorean  center  of  accumulation  and  formed  a  very  extensive  advance 
reaching  into  Iowa,  Illinois,  Indiana,  Ohio,  Pennsylvania  and  cov- 
ering practically  all  of  New  York  and  the  New  England  states. 
This  glacier  built  up  a  system  of  moraines  in  the  middle  west  that 
is  one  of  the  most  characteristic  features.  The  terminal  moraine 
of  the  greatest  advance  is  usually  a  distinct  ridge.    In  Illinois  and 
Indiana  it  is  known  as  the  Shelbyville  moraine.    This  glacier  made 
several  advances  and  recessions,  building  up  a  moraine  with  each 
advance,  giving  a  series  somewhat  concentric  with  Lake  Michigan 
and  other  Great  Lakes.     A  deposit  of  loess  covers  this  drift  in 
Illinois  and  parts  of  Indiana  to  a  depth  of  from  three  to  six  feet. 
This  glaciation  was  followed  by  a  comparatively  short  unnamed 
interglacial  stage. 

(f)  Late  Wisconsin  Glaciation. — This  stage  was  terminated 
by  an  ice  advance,  the  late  Wisconsin,  from  all  centers  of  accumula- 
tion and  in  addition  from  many  local  centers.     It  was  one  of  the 
mpst  extensive  and  uniform  ice  sheets  during  the  entire  glacial 
period.     The  ice  front  did  not  extend  southward  as  far  as  some 
other  advances  except  in  Xew  England,  but  there  was  probably  a 
solid  ice  front  from  the  Atlantic  to  the  Pacific.     The  erosive  and 
transporting  power  of  the  ice  seemed  to  have  been  greatest  at  this 
time,  as  is  shown  by  the  very  high  and  characteristic  moraines 
formed  near  some  of  the  Great  Lakes. 

Incidental  Features. — Certain  incidental  features  were  de- 
veloped in  connection  with  the  glaciers  that  served  to  modify  the 
soils  in  many  regions.  The  drainage  from  the  melting  ice  during 
part  of  the  time  was  entirely  to  the  south.  The  streams  were  flooded 
and  overloaded  with  sediment,  the  deposition  of  which  built  up  ter- 
races of  gravel,  sand,  silt,  and  even  clay.  When  the  glacier  had  re- 
ceded so  that  the  region  in  northern  United  States  was  partly  cov 
ered,  the  outlet  of  the  lakes,  which  is  naturally  to  the  north  and 
northeast,  was  obstructed  so  that  they  overflowed  the  margin  of  the 
basins  and  drained  into  the  Mississippi  River.  Lake  Agassiz,  the 
enlarged  I^ake  Winnipeg,  is  responsible  for  the  soils  of  the  Red  River 


GLACIAL  OR  ICE-LAID  DEPOSITS 


51 


valley.  (Fig.  41).  Lake  Chicago,  the  axtension  of  Lake  Michigan, 
Lake  Maumee,  an  extension  of  l^ake  Erie,  and  other  lakes  at  Green 
and  Saginaw  Bays  produced  lake-laid  soils  and  formed  characteristic 
beaches. 

The  material  deposited  by  the  glaciers  is  of  every  grade  from 
the  finest  clay  to  boulders  weighing  many  tons  (Fig.  46).    Its  value 


Fio.  46. — Granite  boulder  weif?hini;  about  30  tons,  at  dopot  of  Northwestern  R.  R., 
Waukejtan,  111. 


Fio.  47. — Heap  of  boulders  collected  from  a  moraine  in  northern  Illinois 
(R.  W.  Dickenaon  ) 


52  SOIL  PHYSICS  AND  MANAGEMENT 

for  forming  soils  depends  upon  its  fineness  and  the  rocks  from 
which  it  was  derived.  Many  areas  known  as  boulder  belts  contain 
so  many  boulders  that  it  is  impossible  to  cultivate  the  soil,  while 
in  others  they  were  not  so  abundant  but  that  it  is  practicable  to  re- 
move them.  These  boulders  are  sometimes  used  for  making  fences, 
or  piled  up  on  waste  land  (Fig.  47). 

In  many  cases  where  the  glacier  passed  over  rather  soft  rocks, 
such  as  sandstones  or  shales,  large  amounts  of  this  were  picked  up 
and  pushed  along  and  sometimes  formed  a  very  large  part  of  the 
deposit.  The  soil  formed  from  it  is  very  inferior.  Where  the  crys- 
talline rocks,  such  as  granites  and  syenites,  are  mixed  with  lime- 
stones a  very  fertile  soil  results. 

Most  of  the  boulder  clay  is  sufficiently  fine  for  good  soils,  al- 
though nearly  the  entire  glaciated  area  contains  some  boulders. 
In  the  middle  west  the  drift  is  covered  with  a  layer  of  fine  wind-laid 
material. 

QUESTIONS 

1.  What  was  the  extent  of  the  ice  sheet  during  the  glacial  period? 

2.  To  what  extent  was  material  deposited  ? 

3.  What  pressure  did  the  ice  exert? 

4.  How  are  terminal  moraines  formed? 

5.  Distinguish  between  kames,  eskers,  and  drumlins. 

6.  Name   and  locate  the  centers  of  accumulation   in  North  America  and 

Europe. 

7.  Tell  about  the  Jerseyan  or  Nebraskan  glaciation. 

8.  Give  the  facts  In  regard  to  the  Kansan  advance. 

9.  Tell  about  the  lllinoisan  glaciation. 

10.  What  was  characteristic  of  the  lowan? 

11.  What  was  the  extent  of  the  Early  Wisconsin  advance? 

12.  What  was  the  extent  of  the  area  covered  by  the  Late  Wisconsin? 

13.  What  effect  did  this  have  on  drainage? 

14.  Give  some  illustrations. 

15.  What  are  boulder  belts? 

16.  What  was  the  general  effect  of  glaciers  on  soils?     On  topography? 

17.  What  is  boulder  clay? 

REFERENCES 

1Levprett,   F.,   Illinois   Glacial   Lobe,   Monograph    38,   U.   S.   Geol.    Survey, 
1899,  p.  549. 

General  References. — Leverett  and  Taylor.  Monograph  53,  I'.  S.  Geol. 
Survey,  The  Pleistocene  of  Indiana  and  Michigan  and  the  History  of  the 
Great*Lakes,  1915,  op.  Tit.  Complete  Bibliography,  pp.  33-54.  Chamberlain 
and  Salisbury,  Geology,  volume  iii.  Earth  History,  The  Cause  of  the  Glacial 
Period,  pp.  424-440.  Wright,  G.  F.,  The  Ice  Age  of  North  America  and  Its 
Bearintr  on  the  Antiquity  of  Man,  New  York,  4th  ed.,  1890,  pp.  vii-xxv, 
315-358. 


CHAPTER   V 

THE  PLACING  OF  SOIL  MATERIAL  (Continued) 
III.  EOLIAL  OR  WIND-LAID  DEPOSITS 

THE  statement  has  been  made  that  every  square  mile  on  the 
earth's  surface  has  received  particles  from  every  other  square  mile. 
Whether  this  is  absolutely  true  or  not,  it  shows  that  a  very  wide 
distribution  of  material  has  been  going  on,  and  this  distribution 
has  been  brought  about  by  the  agency  of  wind.  Xo  place  on  the 
earth's  surface  is  free  from  dust.  Even  the  snow  on  the  great 
continental  ice  sheet  of  Greenland  contains  a  perceptible  amount. 
Dust  storms  all  over  the  world  are  carrying  fine  material  into  tho 
upper  atmosphere,  where  it  is  transported  for  thousands  of  miles, 
falling  on  all  parts  of  the  earth.  Dust  falls  have  occurred  in  which 
a  measurable  amount  has  fallen  in  a  few  hours.  In  Indiana  in  1895 
a  snow  fall  was  colored  brown  by  the  large  amount  of  dust  it  con- 
tained. One  sample,  collected  just  after  the  storm,  contained  .37 
per  cent  of  dust  by  weight.  The  same  year  a  sample  of  snow 
collected  in  London  contained  10.05  grains  of  solid  material  per 
gallon  of  water  from  the  melted  snow.  Darwin  observed  that  the 
water  in  tbe  Atlantic  300  miles  from  the  coast  of  northern  Africa 
was  distinctly  colored  by  the  dust,  and  that  dust  was  falling  in  the 
ocean  in  perceptible  quantities  1,(!00  miles  from  the  Desert  of 
Sahara.  The  sirocco  winds  of  the  Sahara  sometimes  carry  dust  in 
perceptible  quantities  as  far  north  as  Scotland.  Professor  J.  A. 
Udden  1  estimated  that  during  an  ordinary  breeze  a  cubic  mile  of 
air  will  contain  225  tons  of  dust,  while  in  a  heavy  storm  it  will 
contain  12(5,000  tons  (Fig.  -IS).  The  dust  picked  up  by  winds 
together  with  that  thrown  into  the  atmosphere  by  volcanoes  has 
played  an  important  part  in  the  formation  of  soils. 

Classes  of  Wind-laid  Material. — The  wind-laid  deposits  are 
dunes,  loess  in  part,  adobe  in  part  and  volcanic  dust. 

1.  Dunes. — Sand  is  the  common  constituent  forming  dunes, 
but  other  materials  sometimes  compose  them,  (lay  and  silt  dunes 
are  not  unusual.  Coffey  -  found  clay  dunes  in  southern  Texas, 
while  silt  dunes  are  frequently  met  with  in  areas  of  deep  loess. 
Many  of  these  are  found  on  the  eastern  borders  of  the  Mississippi 

53 


54 


SOIL  PHYSICS  AND  MANAGEMENT 


and  Illinois  Rivers,  notably  in  Carrol,  Whiteside,  Hock  Island  and 
St.  Clair  Counties  in  Illinois.  The  conditions  necessary  for  the 
formation  of  sand  dunes  are  a  supply  of  sand  and  a  somewhat  high 
and  constant  wind.  Sea  and  lake  shores  furnish  excellent  conditions 
for  the  formation  of  sand  dunes.  The  waves  throw  the  sand  upon 
the  beach  and  the  strong  winds  which  so  often  prevail  there  carry 
it  landward.  Shaler  estimates  that  ninety  per  cent  of  the  coast  line 
of  the  world  is  fringed  with  sand.  The  total  dune  area  of  Europe 
is  4,562,000  acres,  while  the  sand  wastes  add  about  9,000,000  acres 
more. 


Fio.  48. — A  dust  storm  in  Kansas,  May  26,  1912.     (Jardine,  Jour.  Am.  Soc.  Agronomy, 

Vol.  5,  No.  4.) 

Sand  is  not  raised  far  above  the  surface  as  in  the  case  of  dust, 
and  a  shrub,  a  tuft  of  grass  or  a  fence  may  give  lodgment  to  the 
sand  and  origin  to  a  dune.  After  accumulations  have  once  begun  by 
means  of  an  obstruction,  the  dune  itself  will  furnish  the  necessary 
conditions  for  growth.  In  shape,  dunes  may  be  either  in  the  form 
of  hillocks,  crescents,  or  ridges,  transverse  or  parallel  to  the  pre- 
vailing winds.  The  shape  of  the  individual  dune  is  a  steep  leeward 
and  a  gradual  windward  slope,  especially  where  the  prevailing  wind 
is  constantly  from  the  same  direction. 

Sand  dunes  are  of  two  classes,  migratory  or  wandering  (Fig. 
49),  and  permanent  or  fixed.  With  a  constant  wind,  dunes  migrate 
or  advance  a  few  feet  each  year,  burying  objects  in  their  paths. 


EOLIAL  OR  WIND-LAID  DEPOSITS 


55 


Even  villages  and  forests  cannot  withstand  the  advance  of  sand 
dunes.  The  usual  height  is  from  ten  to  thirty  feet,  but  some  have 
been  found  300  feet  high.  Through  some  temporary  change  in 
climate,  as  increased  rainfall  or  diminished  wind  velocity,  vegeta- 
tion may  start  on  the  sand  and  gain  such  a  foothold  that  the  dune 
becomes  fixed  or  permanent.  This  fixed  feature  is  sometimes 


Fia.  49. — Sand  dune  advancing  over  forest,  Beaufort  Harbor,  N.  C.     (U.  S.  Geol.  Survey.) 


Fio.  50. — A  resurrected  forest,  Dune  Park,   Tni!i:inn.     (Chamberlain  and  Salisbury,  Cour- 
tesy Henry  Holt  <fc  Co.) 


56 


SOIL  PHYSICS  AND  MANAGEMENT 


brought  about  by  plantings  on  the  windward  side.  In  Denmark, 
Prussia,  Scotland,  Massachusetts,  and  North  Carolina,  beach  or 
marram  grass  (Fig.  52)  whose  roots  extend  to  a  great  depth 

r 


Fio.  51. — Wind  ripples  on  sand  dune.     (Cross,  Chamberlain  and  Salisbury. 
Henry  Holt  &  Co.) 


Fia.  52.— Transplanting  beach  or  marram  grass.    (Bureau  of  Plant  Industry.) 


EOLIAL  OR  WIND-LAID  DEPOSITS 


57 


FIG.   53. — The  grass  in   the   foreground   holds   the   Band   which   drifts   from   the   "waste" 
beyond  the  fence.     (U.S.  Dept.  of  Agriculture-^ 


Fio.  54. — Sandis  being  held  by  vegetation.    In  thisway  wandering  dunes  may  he  changed 
to  permanent  ones.     (U.  S.  Dept.  of  Agriculture.  1 


58 


SOIL  PHYSICS  AND  MANAGEMENT 


has  been  used  quite  extensively  to  hold  the  eand.  This  grows 
luxuriantly  as  long  as  the  sand  is  drifting,  but  dies  and  is  re- 
placed by  other  forms  of  vegetation  as  soon  as  movement  ceases. 
After  fixation  is  accomplished  certain  varieties  of  trees  may  be 

^ 


Pia.  55. — Fences  being  used  to  check  the  movement  of  sand.    (U.  S.  Dept.  of  Agriculture.) 

planted,  transforming  these  dunes  into  valuable  forest  lands. 
Permanent  or  fixed  dunes  may  be  changed  to  migratory  ones  by 
injudicious  management,  such  as  very  close  grazing,  tillage 
or  anything  that  destroys  or  removes  the  protecting  vegetation. 
This  h&3  occurred  in  some  western  states  where  close  grazing  by 
sheep  has  destroyed  the  vegetation  so  that  sand  movement  has 
begun.  Michigan,  Illinois,  Wisconsin  and  Indiana  have  consid- 
erable areas  of  sand  dunes.  A  large  part  of  these  areas  is  covered 
with  a  scrubby  growth  of  black  oak  and  other  trees,  which  furnish 
complete  protection.  When  this  growth  is  removed,  however,  it 
is  very  difficult  to  hold  the  sand  and  it  is  the  part  of  wisdom  to 
leave  even  the  poor  growth  of  forest  for  purposes  of  protection. 
The  dune  areas  covered  with  prairie  grasses  peculiar  to  the  sand 
present  different  problems.  As  a  general  rule,  there  is  sufficient 
organic  matter  in  the  surface  six  to  eight  inches  to  hold  the  sand 
particles.  When  the  soil  is  cropped  or  pastured,  some  of  this  sur- 
face soil  may  be  removed  by  the  wind  in  exposed  places,  forming 


EOLIAL  OR  WIND-LAID  DEPOSITS 


59 


what  is  called  a  "blowout"  (Fig.  5G).  The  tendency  is  for  this 
to  increase  in  size  and  often  results  in  ruining  large  areas.  To 
reclaim  these  "  blowouts  "  it  is  necessary  to  grow  legumes,  plants 
able  to  take  their  nitrogen  from  the  air.  The  black  locust  (Pig.  57) 


FIQ.  56. — Large  "blowout"  in  sand  area.     Numerous  small  ones  may  be  seen  in  the  dis- 
tance.     Mason  County,  Illinois 


Fio.  57. — Black  locusts  (Robinia  •pseudo  acacia,  L.),  growing  on  sand  to  the  right,  drifting 
sand  mi  left.      (L.  A.  Abbott.) 

is  probably  one  of  the  best,  although  if  the  common  sensitive  plant, 
the  partridge  pea  (Cassia  chamcecrista) ,  can  get  a  start  it  will  stop 
the  movement.  The  trailing  wild  bean  (Fig.  r>S)  is  another  plant 
that  grows  luxuriantly  on  sand  and  does  much  toward  building  up 


60 


SOIL  PHYSICS  AND  MANAGEMENT 


the  soil.  The  particular  advantage  of  this  is  that  it  resecds  itself 
and  follows  ry.e  and  wheat  with  a  good  growth  of  renovating  mate- 
rial. Bunch  grass  grows  very  well  upon  the  blowouts  and  fre- 


Fid.  58. — The  trailing  wild  bean  (Strophoslylcs  he'.vola.  Britton)  makes  a  large 
growth  that  not  only  protects  the  sand  against  blowing  but  adds  organic  matter  and  nitro- 
gen to  the  soil.  Illinois. 


Fio.  59. — Pines  growing  on  sand  dunes  in  England  at  Burry  Port.     (Carmarthen.) 

quently  is  the  means  of  stopping  the  movement.    The  use  of  pines 
for  this  purpose  is  shown  in  figure  59. 

2.  Loess. — Sand  dunes  are  limited  to  regions  where  sand  is 
abundant  and  where  vegetation  does  not  prevent  its  being  moved. 


EOLIAL  OR  WIND-LAID  DEPOSITS  61 

It  is  never  carried  any  distance  by  the  wind  but  is  rolled  along  the 
surface  of  the  ground.  Sand  dunes  rarely  travel  more  than  ten  or 
fifteen  miles.  Finer  material,  however,  may  be  picked  up  by  the 
wind  and  transported  for  hundreds  or  even  thousands  of  miles. 
This  brings  about  a  very  wide  distribution  of  the  finer  soil  material. 
In  many  cases  this  is  carried  in  sufficient  amounts  to  form  deposits 
several  hundred  feet  in  thickness.  This  fine  deposit  has  been  called 
"  loess"  by  the  Germans  and  the  term  is  applied  to  the  same  deposit 
in  this  country.  Loess  is  distributed  over  a  large  area  in  North 
America,  comprising  over  600,000  square  miles,  but  is  really  limited 
to  the  states  bordering  the  Mississippi  River  and  its  tributaries.  Its 
depth  varies  from,  two  to  six  feet  over  the  principal  part  of  this 
loess-covered  area,  but  near  the  larger  streams  reaches  a  depth  of 
25  to  150  feet.  In  Europe  the  loess  is  not  so  generally  distributed  as 
in  North  America,  but  occurs  in  somewhat  isolated  areas  and  seldom 
over  12  feet  in  depth.  It  extends,  however,  from  northern  France 
across  Belgium,  Germany,  Austria,  and  southern  Russia,  where  it 
forms  the  soil  known  as  the  "  black  earth,"  or  chernozem.  It  con- 
tinues eastward  across  Asia  into  China,  where  some  of  the  deepest 
and  most  interesting  deposits  occur  that  are  to  be  found  anywhere. 
This  deposit  covers  an  area  of  400,000  square  miles  in  China,  mostly 
in  the  basin  of  the  Hoang  Ho,  in  places  to  a  depth  of  1,500  to  2.000 
feet.  It  will  be  noticed  that  this  belt  follows  the  temperate  zone. 
Loess  deposits  are  found  in  Argentina  and  South  Africa,  but  little  is 
known  of  their  extent. 

The  origin  of  loess  has  been  much  discussed  and  several  theories 
have  been  advanced,  but  it  is  very  likely  that  no  one  theory  will 
account  for  the  deposit  in  all  cases.  Since  a  careful  study  of  the 
work  of  the  wind  has  been  made  it  is  generally  conceded  that  this 
agency  is  responsible  for  much  the  larger  part  of  the  deposit.  There 
is  little  doubt. but  that  some  loess  may  have  been  deposited  as  a 
sediment  from  water  and  in  some  instances  both  wind  and  water 
have  played  a  part. 

As  evidence  of  its  eolial  origin,  it  is  found  at  all  altitudes  up 
to  5,000  feet  tibove  sea  level  in  Europe  and  probably  as  much  as 
3.500  feet  in  the  Tinted  States.  To  have  this  deposited  by  water 
would  have  required  these  regions  to  have  been  submerged  to  that, 
extent,  and  there  is  no  evidence  of  such  submergence.  The  depth 
of  the  deposit  is  quite  uniform  over  hills  and  valleys  as  if  it  came 
like  a  gentle  snow.  In  the  I'nitcd  States,  where  the  subject  has 
received  much  attention,  it  is  believed  that  the  material  has  been 


62 


SOIL  PHYSICS  AND  MANAGEMENT 


taken  from  the  flood  plains  of  streams  that  carried  the  waters  from 
the  melting  glaciers,  depositing  the  rock  flour  over  the  flooded 
plains  of  these  streams  (Fig.  60).  During  the  cold  part  of  the 
year  the  flood  plains  were  bare  and  dry  and  this  fine  material  was 
carried  over  the  upland  by  the  wind.  The  depth  of  the  deposit 
varies  with  the  width  of  the  flood  plain  from  which  the  material 
was  derived  and  the  distance  from  the  stream.  The  coarser  material 
was  deposited  on  the  upland  adjoining  the  flood  plain,  while  the  finer 
was  carried  to  much  greater  distances.  Near  the  flood  plains  from 
which  it  was  derived  it  was  occasionally  deposited  upon  the  uplands 


Fia.  60. — Alluviation  by  glacial  stream  below  Hidden  Glacier,  Alaska.  This  occurred 
to  a  large  extent  during  the  Glacial  Period.  The  upland  loess  was  derived  from  these  allu- 
vial deposits.  (Chamberlain  and  Salisbury,  Courtesy  Henry  Holt  <fe  Co.) 

in  the  form  of  dunes,  either  as  hillocks  or  ridges.  These  frequently 
show  the  typical  dune  topography.  In  Illinois  and  other  states  we 
find  that  along  the  larger  streams  the  loess  deposit  is  deeper  on  the 
upland  adjoining  the  wide  bottom  lands.  Where  no  bottom  land 
exists,  the  deposit  on  the  adjacent  upland  is  very  thin.  This  indi- 
cates a  very  close  relation  existing  between  the  loess  and  the  botfom 
land.  The  deposit  is  deeper  on  the  east  side  of  the  flood  plains  than 
on  the  west,  indicating  prevailing  westerly  winds  at  the  time  of 
deposition.  Very  much  of  the  loess  of  North  America  was  deposited 
at  the  close  of  the  lowan  glaciation.  The  melting  of  this  glacier 
seems  to  have  been  accompanied,  as  Leverett  says,  by  heavy  periodic 


EOLIAL  OR  WIND-LAID  DEPOSITS 


63 


rainfall  which  caused  floods  that  completely  covered  the  flood  plains. 
These  periods  of  alluviation  were  followed  by  those  in  which  the 
rivers  contracted  to  their  ordinary  channels  and  left  the  sediment 


Fid.  61. — Calcium  carbonate  concretions  (Lueaa  Kindchen),  from  the  loens  of  Illinois. 


Fia.62. — A  roud  through  a  deposit  of  deep  loess  along  the  lower  Illinois  River.    The  deposit 
is  30  to  50  feet  deep.     The  vertical  walls  are  characteristic. 


64 


SOIL  PHYSICS  AND  MANAGEMENT 


to  dry.  It  was  then  picked  up  by  the  wind  and  carried  over  the 
upland.  This  lowan  loess  was  very  extensive,  reaching  as  far  east 
as  southwestern  Ohio,  north  into  Wisconsin,  and  as  far  south  as 
Louisiana  on  hoth  sides  of  the  Mississippi  Jiiver. 

Loess  is  quite  uniform  in  texture,  consisting  primarily  of  par- 
ticles of  silt  mixed  with  fine  sand  and  a  small  amount  of  clay.  Since 
much  limestone  was  ground  up  by  the  glaciers,  the  loess  contains  a 
large  proportion  of  carbonates,  as  much  as  28  per  cent  in  some 
cases.  The  percolating  carbonated  water  has  dissolved  the  car- 
bonate from  the  upper  part  and  carried  it  downward,  depositing  it 
in  the  form  of  concretions  of  various  sizes  and  shapes  as  shown  in 
figure  61.  Some  of  these  are  tubular.  It  is  probable  that  these  were 
formed  in  the  openings  left  after  roots  had  decayed.  Concretions 
of  iron  are  formed  occasionally. 

The  deeper  loess  deposits  show  characteristic  vertical  cleavage 
and  cuts  through  this  maintain  vertical  walls  for  long  periods  of 
time  (Fig.  (52).  Terrestrial  shells,  such  as  snails,  are  frequently 
found  in  the  deeper  deposits,  with  an  occasional  fresh  water  shell. 

The  following  table  gives  the  analysis  of  loess  from  different 
sources  for  comparison  with  a  dust  fall  in  Indiana: 


Physical  Analysis  of  Loess  ami  Dust  *  (Grades  of  Bureau  of  Soils) 


Constituents 

Upland  loess, 
Virginia  City, 
Illinois 

River  loess, 
Virginia  City, 
Illinois 

Loess, 
Nebraska 

Dust  from 
snow,  Rook- 
ville,  Indiana 

Moisture           

per  cent 

per  cent 

per  cent 
540 

per  cent 
3  17 

Organic  matter  .    ... 

496 

11  98 

Gravel               .    .    . 

0.00 

000 

000 

0  00 

Coarse  sand 

000 

000 

000 

ooo 

Medium  sand 

000 

001 

0  00 

000 

Fine  sand  

0.01 

0.10 

000 

000 

Very  fine  sand  

7.68 

24.84 

23  14 

000 

Silt  

(51.85 

60.98 

5481 

69  37 

Fine  silt 

960 

280 

2  46 

5  80 

Clay 

1")  15 

6  15 

9  45 

9  68 

Total  

94.29 

94.88 

99.22 

10000 

The  chemical  analysis  of  five  samples  from  different  places  is 
given  in  the  next  table.  Note  the  amount  of  lime  and  magnesia. 
The  deposit  is  usually  characterized  by  a  large  amount  of  car- 
bonate. 


EOLIAL  OR  WIND-LAID  DEPOSITS 


65 


Chemical  Analyses  of  Loess  from  Various  Sources  * 


Constituent! 

Galena, 
Illinois 

Kansas 
City, 
Missouri 

Vicksburg, 
Mississippi 

Valley 
of  the 
Rhine 

Neubad, 
Switserland 

Silica  (SiOj)  

IK.T  cent 

64.61 

ptr  cent 

74.46 

per  cent 
60.69 

per  cent 

58.97 

per  cent 

71.09 

Alumina  (ALjO»)    

10.64 

12.26 

7.95 

9.97 

) 

Iron  sesquioxide  (FejO»)  .  . 
Iron  protoxide  (FeO) 

2.61 
0.51 

3.25 
0.12 

2.61 
067 

4.25 

|  16.78 

Titanium  oxide  (TiOi)..  .  . 

0.40 

0.14 

0.52 

Phosphoric        anhydride 
(P,O6)  

0.06 

0.09 

0.13 

0.11 

Manganese  oxide  (MnO)  . 
Lime  (CaO)  

0.05 
5.41 

0.02 
1.69 

0.12 
8.96 

iiisi 

i.si 

Magnesia  (MgO)  

3.69 

1.12 

4.56 

2.04 

None 

Soda  (Na»O)  

1.35 

1.43 

1.17 

084 

1.23 

Potash  (K2O)  

2.06 

1.83 

1.08 

1.11 

1.30 

Water  (H,O)  

2.05* 

2.70* 

1.14* 

1.371 

1.96 

Carbon  dioxide  (COj)  
Sulfurou3  anhydride  (SO») 
Carbon  (C)  

6.31 
0.11 
0.13 

0.49 
0.06 
0.12 

9.63 
0.12 
0.19 

11.08 

0.80 
•  2!87t 

Total.  .  , 

99.99 

99.78 

99.54 

100.94 

97.95 

*  Contains  H  of  organic  matter. 
t  Organic  matter  dried  at  100°  C. 
t  Ignition. 

3.  Adobe. — Adobe  is  a  calcareous  clay  of  a  gray,  gray-brown 
or  dull  yellowish  color,  very  fine  grained  and  porous,  friable  and  yet 
standing  in  vertical  escarpments  for  many  years.     The  adobe  soils 
are  found  in  the  arid  and  semi-arid  regions  and  represent  both  wind 
and  water  deposits.    Much  of  the  adobe  was  undoubtedly  formed  in 
shallow  lakes  by  the  deposition  of  very  fine  material  which  con- 
tained a  large  amount  of  carbonate,  resembling  loess  in  this  respect. 
Professor  Russell r>  speaks  of  this  deposit  as  assorted  and  spread  out 
over  the  valley  bottom  by  the  action  of  ephemeral  streams  where  it 
becomes  mixed  with  dust  blown  by  the  winds  from  the  neighboring 
mountains  and  rendered  more  or  less  coherent  by  the  cementing 
action  of  carbonate  of  lime.     It  occurs  from  Mexico  northward  to 
Oregon  and  Idaho  and  from  California  to  Colorado.     In  altitude  it 
varies  from  sea  level  in  Arizona  to  8,000  feet  and  in  thickness  from 
a  few  feet  to  3,000  feet  or  more. 

4.  Volcanic    Dust. — During    the   explosive   eruptions   of   vol- 
canoes large  quantities  of  dust  and  ashes  are  thrown  into  the  air 
which  may  be  carried   long  distances  by  the  wind.        Volcanoes 
existed  formerly  where  no  active  ones  are  found  at  present.    Xorth- 
western  United  States  was  a  region  of  great  volcanic  activity  in 


66  SOIL  PHYSICS  AND  MANAGEMENT 

comparatively  recent  geologic  time.  As  a  result  of  this  action,  large 
deposits  of  volcanic  dust  are  found  in  Washington,  Oregon,  Idaho, 
Montana,  Wyoming,  and  Nebraska.  In  the  latter  state  the  deposit 
varies  from  4  to  30  feet  in  thickness,  while  in  some  of  the  north- 
western states  the  deposit  is  much  deeper.  To  give  some  idea  of  the 
amount  of  dust  that  is  transported  by  the  wind  during  a  volcanic 
eruption,  and  the  distance  to  which  it  may  be  carried,  it  is  said  that 
the  dust  from  a  volcano  in  Nicaragua  was  distributed  by  the  wind 
over  1,500,000  square  miles  and  that  ashes  from  Krakatoa  fell  to 
a  depth  of  several  inches  at  a  distance  of  a  thousand  miles  from 
the  volcano. 

QUESTIONS 

1.  Give  some  examples  of  dust  falls. 

2.  Give  classes  of  wind-laid  material. 

3.  Where  are  sand  dunes  found  and  what  is  the  source  of  the  sand? 

4.  What  is  the  shape  of  sand  dunes?    How  may  they  vary  from  this? 

5.  How  is  sand  movement  stopped  on  the  shores? 

6.  How  may  fixed  dunes  be  changed  to  wandering  onea? 

7.  What  is  a  "  blowout "  ? 

8.  What  special  advantage  does  beach  grass  have  tor  preventing  drifting  of 

sand? 

9.  Where  are  loess  deposits  found? 

10.  Give  reasons  for  believing  that  loess  is  a  wind  deposit. 

11.  Do  dust  particles  carry  a  film  of  air? 

12.  If  so,  what  is  the  effect  of  this  on  the  specific  gravity  of  the  particle? 

13.  What  are  some  of  the  characteristics  of  loess? 

14.  How  does  it  compare  with  dust? 

15.  Give  characteristics  of  adobe. 

16.  Where  is  it  found? 

1?.  How  extensive  are  deposits  of  volcanic  dust? 

REFERENCES 

1  UddeU,  J.  A.,  Popular  Science  Monthly,  September,  188(5. 
"Coffey,  G.  N.,  Journal  of  Geology,  vol.  xvii,  No.  8,  1909. 

*  Merrill,  G.  P.,  Rocks,  Rock- Weathering  and  Soils,  p.  319. 
4  Op.  Cit.,  p.  318. 

•  Subaerial  Deposits  of  North  America,  Geol.  Mag.,  August,  1889. 

General  Reference.— Free,  E.  E.,  Bulletin  68,  Bureau  of  Soils,  U.  S. 
D.  A.,  The  Movement  of  Soil  Material  by  the  Wind,  with  Bibliography. 


CHAPTER   VI 

SOIL  AND  SUBSOIL 

THE  soil  may  be  conveniently  divided  into  two  strata:  (1)  the 
top  soil,  consisting  of  (a)  surface  0  to  6%  inches  and  (b)  subsur- 
face 6%  to  20  inches,  and  (2)  subsoil,  which  extends  to  an  indefi- 
nite depth,  but  is  sampled  from,  20  to  40  inches.  The  difference 
between  the  two  divisions,  the  top  soil  and  subsoil,  is  mainly  due  to 
the  action  of  organisms,  both  plants  and  animals,  although  physical 
and  chemical  agencies  have  played  no  inconsiderable  part  in  pro- 
ducing these  differences. 

1.  The  Top  Soil. —  (a)  Surface. — The  surface  soil  is  confined 
to  the  part  usually  turned  by  the  plow  and  is  the  stratum  with 
which  the  farmer  is  most  familiar.  Organic  matter  and  fertilizers 
are  incorporated  in  this  stratum  and  for  this  reason  the  roots  of 
our  common  crops  are  largely  confined  here.  The  most  obvious  dis- 
tinction in  nxost  soils  between  this  and  any  other  layers  is  the 
darker  color  produced  by  the  larger  content  of  organic  matter  or 
humus.  This  brings  about  decided  color  changes,  sucli  as  darkening 
when  moistened.  Hydrated  ferric  oxide,  if  very  abundant,  may 
obscure  the  dark  color  of  organic  matter. 

The  surface  soil  frequently  differs  from  the  other  strata,  and 
more  particularly  the  subsoil,  in  being  made  up  of  slightly  coarser 
material.  This  difference  is  not  found  in  arid  regions.  It  is  due 
to  the  washing  downward  of  the  fine  particles  by  percolating  water, 
as  well  as  by  their  removal  through  surface  run-off  during  heavy 
showers.  This  stratum  contains  the  largest  amount  of  fertility  but 
generally  the  least  of  lime.  Organisms  of  all  kinds,  usually  found 
in  soils,  are  more  abundant  in  this  layer.  Here  are  found  the  most 
favorable  condition's  for  bacterial  growth  and  activity.  The  germs 
of  fungous  diseases,  if  present  in  the  soil,  are  more  abundant  in 
this  stratum.  It  is  the  only  part  of  the  soil  that  we  can  change 
materially  and  hence  its  importance. 

(b)  Subsurface. — The  subsurface  stratum  lies  between  the  sur- 
face and  the  subsoil,  but  usually  resembles  the  surface  more  closely 
than  it  does  the  subsoil.  The  stratum  is  a  natural  one,  extending 
from  the  plowed  soil  to  the  line  where  the  change  in  color,  physical 
composition  and  structure  indicates  the  beginning  of  the  subsoil. 

67 


68  SOIL  PHYSICS  AND  MANAGEMENT 

The  thickness  of  this  stratum  varies  from  0  to  30  inches  and  even 
more,  as  in  the  case  of  peat  and  other  swamp  soils.  That  of  normal 
upland  loessial  soils  is  from  eight  to  ten  inches. 

The  amount  of  organic  matter  decreases  with  depth  and  varies 
with  that  of  the  surface  soil.  Under  normal  conditions  it  is  never  as 
abundant  as  in  the  surface  because  the  root  development  is  never 
so  great  and  the  chances  for  the  introduction  of  other  vegetable 
material  are  not  so  good.  Exceptions  sometimes  occur  in  alluvial 
land.  The  same  downward  movement  of  fine  material  has  taken 
place  as  in  the  surface  soil,  thus  giving  a  slightly  coarser  texture 
than  in  the  subsoil.  The  subsurface  may  be  made  of  distinct  layers 
that  differ  in  color  or  texture  or  both.  The  color  in  prairie  soil  is 
usually  due  to  organic  matter,  while  in  timber  soils  it  is  principally 
due  to  iron  in  some  form. 

2.  Subsoil. — The  subsoil  extends  to  an  indefinite  depth,  but  is 
sampled  to  40  inches  in  humid  climates.  This  stratum  is  of  great 
importance  because  drainage,  capillary  movement,  root  penetration 
and  resistance  to  drouth  depend  largely  upon  its  character,  and  this 
in  turn  depends  largely  upon  its  origin.  If  residual,  its  character 
will  vary  with  the  parent  rock  from  which  it  was  derived.  It  will 
be  uniform  if  the  parent  rock  was  massive,  and  variable  if  the 
parent  rock  was  formed  of  strata  of  widely  differing  mineral  and 
physical  composition.  In  cumulose,  lacustrine,  glacial  and  alluvial 
deposits,  the  subsoil  is  likely  to  vary  to  almost  any  extent.  There 
may  be  substrata  of  gravel,  sand,  silt,  clay  and  even  peat  with  all 
their  variations.  In  loessial  deposits  two  distinct  layers  usually 
occur  in  the  subsoil,  the  upper  from  6  to  15  inches  thick  consisting 
of  a  clayey  silt  or  a  silty  clay,  formed  by  the  fine  material  carried 
downward  from  the  upper  strata  by  water  and  deposited  in  the 
upper  subsoil,  and  the  lower  composed  largely  of  silt  and  very  fine 
sand,  the  very  pervious  ordinary  loess.  Subsoils  are  usually  less 
pervious  and  more  retentive  of  moisture  than  other  strata. 

Tight  Clay. — All  soils  in  humid  climates  permit  more  or  less 
water  to  percolate  through  them.  When  a  rain  falls  water  passes 
into  the  soil  through  cracks,  burrows,  along  roots  and  through  the 
pore  spaces,  carrying  with  it  a  small  amount  of  very  fine  clay  and 
some  iron  oxide  to  the  depth  of  percolation.  In  time  the  deposition 
of  this  fine  material  between  the  coarser  particles  may  produce  a 
very  heavy,  dense  stratum,  reducing  the  pore  space  to  such  an  extent 
as  to  make  it  almost  impervious  to  air  and  water.  This  is  especially 
liable  to  take  place  in  acid  soils  where  no  lime  is  present  to  precipi- 


SOIL  AND  SUBSOIL  69 

tate  or  flocculate  the  suspended  clay.  These  tight  clay  soils  are 
found  in  Southern  Illinois,  Missouri,  Arkansas  and  many  other 
places. 

The  tight  clay  layer  becomes  very  hard  when  dry,  but  when 
saturated  with  water  it  is  very  soft  and  posts  may  be  driven  into 
it  easily. 

The  tight  stratum  prevents  underdrainage  and  the  topography 
is  almost  invariably  too  flat  for  surface  drainage.  Damage  to  crops 
by  water  is  very  liable  to  occur.  To  remove  the  excess,  plowing  is 
done  in  small  lands,  the  dead  furrows  are  left  open  and  by  this 
means  water  may  be  removed,  especially  since  these  furrows  are 
usually  connected  with  a  ditch  at  the  end  of  the  field.  This  tight 
stratum  very  seriously  interferes  with  the  capillary  movement.  The 
tight  layer  limits  the  storage  of  water  to  that  part  of  the  soil  above 
it.  Even  if  water  is  abundant  below,  it  is  cut  off  because  the  roots 
cannot  penetrate  this  stratum  and  capillary  movement  through  it  is 
so  extremely  slow  as  to  furnish  but  a  scanty  supply,  with  the  result 
that  crops  are  seriously  affected  by  drouth.  The  effect  of  tight  clay 
is  very  difficult  to  overcome.  For  the  permanent  improvement  of 
soils  of  this  kind,  large  applications  of  ground  limestone,  four  to 
six  tons  per  acre,  with  the  growing  of  deep  rooting  crops,  such  as 
red,  mammoth  or  sweet  clover,  are  recommended.  The  puncturing 
of  the  tight  clay  by  these  roots  will  without  doubt  produce  better 
conditions  of  drainage  and  aeration.  Dynamite  is  sometimes  used 
to  break  up  the  tight  clay,  but  this  method  is  too  expensive  for  gen- 
eral farm  use  and  besides  the  subsoil  runs  together  again  when 
.saturated.  The  loess  beneath  this  tight  clay,  which  is  from  eight 
to  twelve  inches  thick,  is  ideal  in  physical  composition. 

Hard  Pan. — Hard  pan  proper  is  formed  by  the  deposition  of 
substances  from  solution  around  soil  particles  cementing  them  to- 
gether into  a  more  or  less  stony  mass.  The  deposition  of  ttiis 
cementing  substance  is  due,  possibly,  to  the  stoppage  of  percolation 
by  an  impervious  stratum,  evaporation  brought  about  by  some  cause, 
or  loss  of  carbon  dioxide,  causing  precipitation,  as  in  the  case  of 
lime  carbonate.  The  cementing  material  is  usually  derived  from 
the  decomposition  of  rocks  and  may  consist  of  such  substances  as 
iron,  magnesia,  lime  or  sodium  carbonate  and  sodium  chloride. 

Since  the  cause  of  hard  pan  is  the  stoppage  of  water  in  its 
movement  downward  the  renewal  of  percolation  will  be  sufficient 
frequently  to  destroy  the  hard  stratum.  If  not  too  deep  it  may  be 
broken  with  plow  or  subsoil  plow,  but  if  beyond  the  reach  of  these 


70  SOIL  PHYSICS  AND  MANAGEMENT 

implements  dynamite  must  bo  resorted  to.  In  planting  trees  on 
hardpan  land  dynamite  may  be  used  and  tbus  allow  tbe  roots  their 
usual  penetration.  If  the  hardpan  is  caused  by  sodium  carbonate, 
it  may  be  necessary  to  apply  gypsum  to  destroy  this  carbonate  and 
thus  break  up  the  hardpan. 

Humid  and  Arid  Subsoils. — The  subsoils  of  arid  regions  do 
not  differ  materially  from  the  surface  and  subsurface  because  the 
fine  particles  are  not  moved  downward  to  any  extent  by  percolating 
water.  In  addition  to  this,  soluble  substances  are  present,  which 
flocculate  the  collodial  clay  and  prevent  its  movement  downward. 
The  arid  subsoils  do  not  possess  the  "  raw  "  or  unproductive  nature 
that  characterizes  the  humid  ones.  In  arid  regions  very  deep  plow- 
ing may  be  done  immediately  preceding  the  planting  of  the  crop 
without  detriment;  in  fact,  it  is  of  great  benefit,  because  it  allows 
deeper  root  penetration  and  greater  moisture  retention.  In  the 
process  of  leveling,  preparatory  to  irrigating,  the  soil  is  sometimes 
removed  to  a  depth  of  several  feet  without  injurious  effect  on  the 
crop  that  follows.  In  humid  regions  the  farmer  must  be  careful 
not  to  turn  up  much  of  the  "raw"  unweathered  material,  just 
preceding  time  of  planting  the  crop,  but  if  deep  plowing  is  done 
sufficient  time  should  be  given  for  the  soil  to  "  weather  "  before 
the  crop  is  put  in.  This  is  probably  partly  due  to  biological 
conditions. 

The  color  differences  do  not  obtain  in  the  arid  regions  because 
the  organic  matter  is  derived  almost  entirely  from  roots,  and  these 
penetrate  very  deeply ;  so  there  is  no  great  accumulation  of  organic 
matter  in  the  surface  stratum.  Oxidation  of  iron  has  not  generally 
gone  very  far  because  of  lack  of  moisture,  hence  arid  soils  are  not 
usually  highly  colored. 

Plow  Sole. — Where  plowing  takes  place  at  a  somewhat  uniform 
depth  for  a  long  time,  the  tramping  of  horses  and  the  sliding  action 
of  the  plow  in  the  bottom  of  the  furrow  have  a  tendency  to  form  a 
compact  layer  or  plow  sole.  The  washing  of  the  fine  material  from 
the  loose,  plowed  soil  down  on  the  furrow  bottom  tends  to  increase  . 
the  tightness  of  the  plow  sole.  In  order  to  break  up  this  stratum 
and  prevent  the  formation  of  another,  plowing  should  be  done  at 
variable  depths,  and  when  the  moisture  condition  is  such  that  pud- 
dling will  nrt  take  place. 


SOIL  AND  SUBSOIL  71 

QUESTIONS 

1.  What  are  the  moat  obvious  differences  between  the  surface  stratum  and 

others? 

2.  What  agencies  have  been  instrumental  in  producing  these? 

3.  What  are  the  upper  and  lower  limits  of  the  subsurface  stratum? 

4.  Under  what  conditions  might  the  subsurface  be  absent? 

5.  What  differences  between  it  and  the  surface? 

6.  Why  is  the  subsoil  of  much  importance? 

7.  Upon  what  do  the  differences  in  subsoils  largely  depend? 

8.  What  is  the  origin  of  the  tight  clay  stratum? 

9.  Where  are  they  found? 

10.  Does  limestone  aid  or  prevent  their  formation? 

11.  What  are  some  objections  to  tight  clay? 

12.  What  are  the  methods  of  improvement? 

13.  How  is  hardpan  formed? 

14.  How  may  hardpan  be  destroyed? 

15.  Give  differences  in  subsoils  of  humid  and  arid  regions. 

16.  What  is  meant  by  "raw"  soil  material? 

17.  What  effect  does  weathering  have  on  subsoil? 

18.  How  do  humid  and  arid  soils  differ  in  color?     Why? 

19.  How  is  a  plow  sole  formed? 

20.  What  are  the  remedies  for  it? 


CHAPTER  VII 

CLASSIFICATION  OF  SOILS 

Need  of  Classification. — The  formation  of  soils  by  means  of 
the  various  agencies  described  has  given  rise  to  great  complexity. 
As  in  any  other  natural  group  of  objects,  the  study  of  the  relation- 
ship existing  between  the  different  members  of  the  group  is  neces- 
sary for  a  complete  understanding  of  them.  This  brings  about  com- 
parison and  classification.  A  very  simple  assumption  would  be  that 
all  soils  derived  from  the  same  kind  of  rocks  are  the  same.  They 
do  usually  have  some  points  of  similarity,  but  so  many  modifying 
factors  have  been  at  work  that  important  differences  are  produced 
even  in  these.  It  must  be  remembered  that  ,soils  are  very  complex 
bodies,  due  to  the  infinite  variety  of  rocks  from  which  they  are 
derived  and  the  large  number  of  agencies  taking  part  in  their 
formation. 

By  far  the  larger  portion  of  soil  material  is  moved  from  fhe 
place  of  its  origin  for  varied  distances,  perhaps  hundreds  of  miles. 
In  its  travels  it  may  be  deposited  over  and  over  again,  and  as  a 
general  rule  the  loose  surface  of  the  earth  is  a  mass  of  drifting 
material,  here  to-day  and  a  hundred  or  even  a  thousand  miles  from 
here  in  the  next  geological  age. 

BASIS  OF  CLASSIFICATION 

1.  Geological. — Soil  is  a  geological  formation  derived  from 
rocks  by  geological  forces.  It  is  very  natural,  then,  that  the  geo- 
logical formation  should  be  used  as  the  basis  of  classification.  A 
number  of  States  have  made  general  soil  maps,  basing  the  areas 
upon  the  geology.  In  many  cases  this  may  serve  a  good  purpose,  as 
where  the  soils  are  closely  related  to  the  underlying  geological  for- 
mation. In  other  places  the  same  formation  may  give  rise  to  a 
great  variety  of  soils,  and  in  this  case  a  classification  on  a  geological 
basis  would  mean  nothing.  In  extensive  glaciated  regions  the  soil 
usually  bears  little  or  no  relation  to  the  geological  formations 
beneath  the  drift.  General  soil  divisions  may  be  based  upon  the 
geological  agencies  that  have  produced  them,  and  in  this  way  form 
an  important  factor  in  classification.  This  gives  rise  to  residual, 
glacial,  loessial,  alluvial,  and  other  formations. 
72 


CLASSIFICATION  OF  SOILS  73 

2.  Lithological. — In    many    cases    soils    have    been    classified 
according  to  the  rocks  from  which  they  have  been  derived  or  upon  a 
lithological  basis.    Kocks  of  the  same  name  are  so  different  in  com- 
position and  are  exposed  to  so  many  and  such  varying  conditions 
and  agencies  of  change  that  they  may  give  rise  to  very  different 
soils.    A  soil  derived  from  a  granite  may  be  very  fertile  under  one 
set  of  conditions  or  almost  absolutely  sterile  under  another. 

3.  Temperature. — Besides  breaking  down  rocks  into  soil  mate- 
rial and  aiding  solution  slightly,  heat  does  not  play  such  an  impor- 
tant part  directly  in  the  formation  of  soil,  but  indirectly  through 
its  effect  and  influence  upon  other  agencies,  temperature  is  of  the 
greatest  importance.     Moderately  high  temperatures  influence  the 
growth  of  plants  and  bacterial  action  as  manifested  in  oxidation 
and  humification  of  organic  matter.    This  brings  about  most  impor- 
tant physical,  chemical,  and  biological  differences.     On  the  basis 
of  temperature  soils  may  be  divided  into  (a)  tropk-,  (b)  subtropic, 
(c)  temperate,  (d)  subarctic,  and  (e)  arctic.     These  are  only  very 
general  and  have  but  little  significance  in  a  system  of  classification. 

4.  Moisture. — Moisture  is  not  only  a  very  important  factor  in 
breaking  down  rocks  into  soil  material,  but  it  brings  about  very 
fundamental  changes  in  the  soils  themselves,  both  chemically  and 
physically.     The  presence  of  moisture  is  necessary  for  all  chemical 
changes,  hence  decomposition  of  minerals  can  take  place  only  when 
water  is  present.     It  is  usually  accompanied  by  the  formation  of 
soluble  compounds  that  are  leached  out  and  carried  away,  and  fre- 
quently to  such  an  extent  as  to  leave  the  soil  deficient  in  plant  food. 

Soils  are  sometimes  divided  into  arid,  where  the  annual  precipi- 
tation is  less  than  10  inches;  semi-arid,  10  to  20  inche-*;  sub-humid, 
20  to  30  inches;  humid,  more  than  30  inches,  and  super-humid, 
including  swamps.  There  can  be  no  distinct  line  of  difference 
between  the  soils  of  such  groups.  In  some  parts  of  India,  with 
a  rainfall  of  28  inches,  the  conditions  are  extremely  arid  because  the 
rainfall  comes  in  a  very  few  niontbs  and  as  torrential  showers, 
resulting  in  much  loss  by  run-off.  The  evaporation  is  very  great 
during  the  rest  of  the  year.  In  parts  of  Texas,  with  a  rainfall  of 
30  inches,  it  is  much  more  arid  than  in  North  Dakota  with  the  same 
rainfall,  because  of  the  character  of  the  rainfall  and  the  greater 
evaporation  in  the  former. 

Great  differences  exist  between  soils  of  arid  and  humid  regions, 
primarily  due  to  the  amount  of  rainfall.  The  moisture  as  well  as 
the  tempejature  influences  the  amount  and  character  of  organic 


74 


SOIL  PHYSICS  AND  MANAGEMENT 


matter  in  soils.  The  presence  of  water  in  large  amounts  arrests 
decomposition,  as  in  swa'mps,  by  excluding  oxygen,  while  its  presence 
in  moderate  quantities  stimulates  nitrification  in  drained  land.  In 
its  movement  downward  through  a  soil,  water  not  only  carries 
soluble  compounds  with  it,  but  moves  the  fine  particles  downward, 
thus  producing  differences  in  physical  composition  in  the  different 
strata. 

(a)  Arid  Soils. — The  agencies  of  disintegration  predominate 
over  those  of  decomposition  in  arid  regions  As  a  result  the  soils  are 
characterized  by  large  amounts  of  original  minerals  that  have  been 
changed  very  little. 

Mineral  Content  of  Soils  l 


Region 

Number  of 
samples 

Minerals  other  than  quart* 
in  the 

Sand 

Silt 

Arid  

30 
40 
160 

per  cent 

37 
20 

8 

per  cent 

39 

29 
12 

Prairie  (subhumid  and  humid)  

Timber  (humid)  

The  great  agency  in  chemical  changes  of  rocks  is  water,  and  its 
deficiency  in  arid  regions  has  protected  the  minerals  from  those 
profound  changes  that  take  place  in  humid  regions.  The  minerals 
have  been  broken  down  into  rather  fine  material,  but  not  into  clay, 
which  results  largely  from  decomposition.  Silt  and  various  grades 
of  sand  predominate.  Their  mineral  content  is  indicated  in  the 
above  table. 

The  low  rainfall  renders  any  large  amount  of  leaching  impos- 
sible, so  that  the  soluble  salts  formed  during  the  limited  decomposi- 
tion remain  in  the  soil.  They  may  be  moved  downward  to  some 
extent  by  the  water,  but  when  evaporation  takes  place  they  are 
brought  to  the  surface  again.  If  excessive  evaporation  occurs  these 
salts  may  be  brought  to  the  surface  in  sufficient  quantities  to  be 
quite  injurious  as  "  alkali." 

Soluble  Salts  in  Soils  * 


Per  cent 


Arid 

Prairie  (subhumid  and  humid). 
Timber  (humid) 


0.333 
0.048 
0013 


CLASSIFICATION  OF  SOILS 


75 


Although  somewhat  easily  soluble,  lime  is  a  very  abundant  con- 
stituent of  soils  of  arid  regions.  The  amount  varies*  from  0.(>9  to 
5.G6  per  cent.  The  table  below  gives  the  average  for  arid  and  humid 
soils. 

Lime  and  Magnesia  in  Soils  of  Different  Regions  * 


Region 

Number  of 
samples 

Per  cent 

Lime  (CaO) 

Magnesia 
(MgO) 

Arid  

318 
215 
743 

2.65 
1.09 
.41 

1.20 
.51 
.37 

Prairie  (subhumid  and  humid)  
Timber   (humid)  

These  arid  soils  are  generally  gray  or  light  in  color,  with  no  very 
decided  change  in  texture  in  the  subsoil.  The  rainfall  is  not  suffi- 
cient to  carry  the  fine  material  downward  in  any  large  amount. 

The  organic-matter  content  of  arid  soils  is  generally  low, 
although  it  contains  a  larger  percentage  of  nitrogen  than  the  organic 
matter  of  humid  regions. 

(b)  Humid  Soils. — In  this  group  of  soils  the  agencies  of 
decomposition  have  predominated  over  those  of  disintegration.  The 
feldspar  and  many  other  minerals  have  largely  undergone  chemical 
change,  producing  the  finer  soil  constituents.  Hence  the  soils  con- 
tain large  amounts  of  clay.  The  subsoil  differs  quite  noticeably  in 
texture  from  the  surface.  Leaching  has  done  very  effective  work 
in  removing  soluble  salts,  as  shown  by  the  second  table  on  page  74. 
Limestone  has  been  leached  out,  and  most  of  the  soils  are  acid  and 
in  great  need  of  this  most  important  constituent.  The  colors  are 
more  highly  developed,  due  to  the  greater  oxidation  of  iron  and  the 
larger  amount  of  organic  matter. 

5.  Vegetation. — Xot  only  do  bacteria,  fungi,  and  alga1  play  a 
very  important  part  in  soil  formation  and  soil  changes,  but  the 
higher  plants,  especially  grasses  and  trees,  exert  a  most  important 
influence  upon  soil  in  several  ways.  They  are  responsible  to  a  very 
large  extent  for  the  amount  of  organic  matter  in  soils.  The  char- 
acter of  the  vegetation  has  given  rise  in  humid  and  subhumid 
regions  to  two  great  groups  of  upland  soils,  (a)  prairie,  and  (b) 
timber  (Fig.  63). 

(a)  Prairie  Soils. — Prairie  soils  are  usually  characterized  by  a 
dark  color,  due  to  a  large  content  of  organic  matter.  The  prairies 
were  covered  with  a  rank  growth  of  grasses  which  produced  a  dense 


76 


SOIL  PHYSICS  AND  MANAGEMENT 


network  of  roots  whose  partial  decay  has  provided  the  soil  with  an 
abundance  of  organic  matter.  This  extends  to  a  depth  of  13  to  24 
inches  in  amounts  sufficient  to  impart  the  predominating  dark  color. 
The  prairie  soils  contain  a  larger  amount  of  lime  than  the  timber 
soils,  and  this  may  be  one  important  factor  in  their  origin.  They 
usually  give  an  alkaline  or  neutral  reaction.  An  exception  to  this 
is  found  in  Southern  Illinois,  some  parts  of  Missouri,  and  Arkansas. 
These  prairies  are  acid  and  have  a  tight  clay  or  so-called  "  hardpan  " 
subsoil. 

Prairie  soils  have  had  sufficient  rainfall  to  leach  out  the  larger 


ana  Tropical  fore  a 

FIG.  63. — Map  of  United  States,  showing  timber  and  prairie  areas.  Unshaded  area, 
Prairie.  Dark  shade  in  Northeast  and  North,  Central  forests.  Lighter  shaded  area  in  South- 
east, Southern  forests.  Very  lightly  shaded  area,  Rooky  Mountain  forests.  Deep  shade, 
Pacific  Coast  forests.  (Graves,  U.  S.  D.  A.  Forest  Service.) 

part  of  the  soluble  salts,  so  that  alkali  is  found  only  in  small  areas, 
and  then  consists  principally  of  the  more  insoluble  magnesium  car- 
bonate. The  second  table  on  page  74  shows  0.048  per  cent  of  solu- 
ble salts  in  prairie  soils,  as  compared  with  0.013  for  timber  soils. 

The  prairie  soils  extend  from  Southern  Texas  northward  into 
Canada,  widening  to  the  east  into  west  central  Indiana.  A  belt  which 
is  not  shown  in  figure  63  extends  across  Mississippi  and  Alabama 
and  over  into  Texas. 

(6)  Timber  Soils. — The  timber  soils  are  characterized  by  a 
lighter  color,  due  to  a  small  amount  of  organic  matter.  This  has 


CLASSIFICATION  OF  SOILS  77 

been  brought  about  by  the  growth  of  forests,  which  place  large  quan- 
tities of  organic  matter,  as  leaves  and  twigs,  on  the  surface  of  the 
soil,  yet  very  little  becomes  incorporated  in  it.  This  material  either 
completely  decays  or  is  burned  by  forest  fires.  The  resulting  soils 
are  light  colored. 

The  relatively  heavy  rainfall  on  timber  soils  has  leached  out  the 
soluble  material,  including  limestone,  so  that  they  are  neutral  or 
acid.  It  is  likely  true  that  the  leaves  have  aided  in  this  process. 

6.  Color. — One  of  the  most  important  factors  in  distinguishing1 
soils  is  that  of  color.     This  is  primarily  due  to  two  things,  organic 
matter  and  compounds  of  iron.     Color  is  a  fair  indication  of  the 
value  of  a  soil.    If  a  large  amount  of  organic  matter  is  present  the 
soil  will  be  black  or  brown,  while  a  smaller  amount  may  be  obscured 
by  the  more  highly  colored  iron  compounds.     Dark  brown  or  black 
soils  are  usually  fertile.     The  color  imparted  by  iron  compounds 
varies  with  the  degree  of  oxidation. 

7.  Texture. — The  size  of  the  soil  particles  and  the  proportion 
of  each  grade  are  the  most  important  factors  in  grouping  soils  into 
classes  and  types. 

QUESTIONS 

1.  Why  are  soils  so  complex? 

2.  Why  should  the  geological   formation  be  used  as  the  basis  of  classifi- 

cation ? 

3.  What  is  the  value  of  a  soil  map  based  upon  the  geological  formation? 

4.  Are  all  soils,  derived  from  the  same  class  of  rocks,  the  same?     Why? 

5.  What  part  does  heat  plav  in  forming  soils? 

6.  What  is  the  significance  of  moisture  in  soil  formation? 

7.  What  are  the  divisions  of  soils  based  on  moisture? 

8.  Why  may  Texas  with  a  30-inch  rainfall  be  more  arid  than  North  Dakota 

with  20  inches? 
J).  What  effect  does  heavy  rainfall  have  on  organic  matter? 

10.  What  agency  predominates  in  the  formation  of  soils  of  arid  regions? 

11.  Why  do  humid  soils  have  a  larger  percentage  of  quart/,  than  arid  soils? 

12.  Why  are  arid  soils  gray  or  light  in  color? 

13.  What  agency  is  most  active  in  the  formation  of  humid  soils? 

14.  Why  do  arid  soils  have  large  amounts  of  earlxinates? 

15.  Why  are  humid  soils  more  highly  colored  than  arid  ones? 

16.  Explain  the  source  of  organic  matter  of  soils. 

17.  (live  differences  Itctween  timl>er  and  prairie  soils. 

18.  Locate  the  large  prairie  region  of  the  United  States. 

19.  Why  do  the  heavy  forests  add  so  little  organic  matter  to  the  soils? 

20.  What  is  the  significance  of  color  in  soil  classification? 

21.  What  is  meant  by  texture  of  a  soil? 

REFERENCES 
1  Coffey.   T,.   X..    A    Study   of   the   Soils   of   the   I'nited   States.    Bulletin    85, 

Bureau  of  Soils.  I".  S.  D.  A.,  p.  15. 
If0p.  Cit.  p.  15. 
•Op.  Cit.  p.  14. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS 

THE  results  of  all  the  preceding  factors  involved  in  soil  changes 
find  expression  and  application  in  the  system  of  classification  devel- 
oped by  the  Bureau  of  Soils.  The  United  States  has  been  divided 
into  13  great  geographic  divisions ;  the  six  in  the  western  part  are 
known  as  soil  regions,  while  the  seven  in  the  eastern  part  are  called 
soil  provinces. 

A  soil  province  is  an  area  which  has  the  same  general  physio- 
graphic expression  and  in  which  the  soils  were  produced  by  the  same 
forces  or  groups  of  forces. 

A  soil  region  may  include  several  soil  provinces  which  later 
study  may  establish.  The  soils  of  a  province  are  grouped  together 
into  series  on  the  basis  of  the  same  range  of  color,  the  same  character 
of  subsoil,  as  regards  color  and  structure,  the  same  type  of  relief 
and  drainage,  and  a  common  or  similar  origin.  A  soil  series  is 
divided  on  the  basis  of  texture  into  classes. 

Soil  Provinces  and  Regions. — Area  Surveyed  up  to  1915 


Provinces 

Estimated 
area 

Detailed 
survey 

Reconnais- 
sance survey 

Total 
are* 

Piedmont  Plateau  

acres 

47,214,000 

acret 

16,638,950 

acret 

2,388,416 

per  cent 

40.3 

Appalachian  Mountain  and 
Plateau            

84,837,000 

19,643,709 

23,509,504 

508 

Limestone  Valley  and  Up- 
land   

67,870,000 

11,660,094 

2,040,896 

20.2 

Glacial  and  Loessial  .   ... 

385,083,000 

43,475,366 

37,724,608 

21.1 

Glacial    Lake    and    River 
Terrace  

442,788,000 

12,956,602 

r,  397,  728 

45.0 

Atlantic  and  Gulf  Coastal 
Plains  

218,362,000 

52,718,882 

22,748,096 

34.6 

River  Flood  Plains  

75,247,000 

26,913,813 

7,561,216 

45.9 

Regions 

Great  Plains  

331,968,000 

13,170,106 

127,711,616 

42.4 

Rocky  Mountains      .    .    . 

265,575,000 

2,674,560 

1  0 

Northwest  Intermountain  . 

75,984,000 

2,322,884 

3.06 

Great  Basin  

118,034,000 

1,399,072 

1.18 

Arid  Southwest  

81,148,000 

1,674,138 

46,080 

2.10 

Pacific  Coast  

109,180,000 

16,953,491 

4,015,360 

19.2 

Total  

1,903,290,000 

222,201,667 

234,043,520 

23.9 

78 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  79 

A  soil  class  includes  all  soils  having  the  same  texture,  such  as 
clays,  peats,  mucks,  clay  loams,  etc.,  and  are  divided  into  soil  types. 

A  soil  type  is  a  soil  which  throughout  the  area  of  its  occur- 
rence has  the  same  texture,  color,  structure,  character  of  subsoil, 
general  topography,  processes  and  sources  of  derivation. 

The  soil  surveys  are  of  two  kinds,  reconnaissance  and  detailed. 
The  former  furnishes  only  general  information,  while  the  latter 
gives  the  soil  types  in  considerable  detail. 

I.  THE  PIEDMONT  PLATEAU  PROVINCE 

The  Piedmont  Plateau  comprises  the  rolling  to  hilly  region 
lying  between  the  eastern  foot  of  the  Appalachian  Mountains  and 
the  Atlantic  Coastal  Plain.  The  northern  end  of  this  province  lies 
in  northeastern  New  Jersey,  along  the  glacial  boundary,  in  the 
vicinity  of  the  Hudson  Kiver.  It  extends  soutliwestward,  and  in 
Virginia  is  a  belt  ranging  from  20  to  50  miles  in  width.  Widening 
here  it  continues  in  a  southwesterly  direction  to  central  Alabama 
with  an  average  width  of  approximately  115  miles.  The  province 
has  a  length  of  900  miles,  and  embraces  an  area  of  approximately 
73,770  square  miles.  The  following  are  the  most  important  series 
of  this  province : 

Alamance  Series. — The  surface  soils  of  this  series  are  gray  to 
almost  white  and  of  silty  texture.  The  subsoils  are  composed  of 
yellow,  rather  compact  silty  clay.  Scattered  over  the  surface  are 
fragments  of  the  parent  rocks  which  belong  to  the  "  Carolina 
slates."  It  forms  a  belt  in  central  North  Carolina,  and  extends  a 
short  distance  into  South  Carolina.  The  topography  varies  from 
nearly  flat  to  rolling,  or  in  some  places  steeply  rolling. 

Cecil  Series. — The  Cecil  series  include  the  most  important  and 
widely  distributed  soils  of  the  Piedmont  Plateau.  The  heavier 
members  are  known  as  the  "  red-clay  lands."  These  soils  are 
residual,  derived  from  gneisses  and  schists  and  characterized  by 
their  red-clay  subsoils  and  gray  to  red  soils,  ranging  in  texture  from 
sand  to  clay,  the  lighter  colors  prevailing  in  the  sandy  members.  A 
characteristic  of  the  subsoil  is  the  content  of  sharp  quart/  sand  and 
the  frequent  occurrence  of  the  remains  of  veins  of  quartx.  Mica 
flakes  are  also  usually  present  in  the  subsoil.  The  topography  is 
slightly  rolling  to  hilly.  The  soils  are  adapted  to  general  farm 
crops  and  in  the  South  to  cotton.  Over  seven  and  one-half  million 
acres  have  been  mapped. 


80  SOIL  PHYSICS  AND  MANAGEMENT 

Chester  Series. — The  Chester  series  occurs  in  the  northern  part 
of  the  Piedmont  Plateau,  having  been  mapped  only  in  Pennsylvania, 
Maryland,  and  Virginia.  The  types  in  this  series  differ  from  those 
in  the  Cecil  series  in  having  yellow  or  only  slightly  reddish  yellow 
subsoils  and  gray  or  brown  surface  soils,  the  latter  being,  on  the 
whole,  lighter  and  more  friable  than  the  Cecil.  Locally  they  are 
known  as  "  gray  lands,"  to  distinguish  them  from  the  "  red  lands  " 
of  the  Cecil  series.  The  soils  are  adapted  to  general  farm  crops 
and  fruit. 

Durham  Series. — The  soils  of  the  Durham  series  are  character- 
ized by  the  grayish  color  of  the  surface  and  the  yellow  color  of  the 
subsoils.  They  are  derived  from  light-colored,  rather  coarse-grained 
granite  and  gneiss,  consisting  principally  of  quartz  and  feldspar, 
with  some  mica. 

Iredell  Series. — The  soils  of  the  Iredell  series  are  light  brown 
to  almost  black  in  color  and  frequently  carry  small  iron  concretions. 
The  subsoils  consist  of  extremely  plastic,  sticky  or  waxy  clay  of  a 
yellowish  brown  to  greenish  yellow  color.  Disintegrated  rock  is 
often  encountered  within  the  three-foot  section.  The  soils  are  best 
suited  to  grain  and  grass. 

Lansdale  Series. — The  Lansdale  series  is  characterized  by  the 
gray,  drab,  or  brownish  color  of  the  soils  and  by  the  slaty  gray  to 
pale  yellowish  color  of  the  subsoil.  They  are  derived  from  metamor- 
phosed Triassic  sandstone  and  shale.  Moderate  yields  of  hay,  corn, 
oats,  wheat,  and  Irish  potatoes  are  secured. 

Louisa  Series. — The  soils  of  this  series  are  predominantly  gray 
to  light  gray  and  the  subsoils  red.  The  material  is  derived  from 
talcose  and  micaceous  schists  and  imperfect  crystalline  slates.  They 
are  suited  to  corn,  grain,  forage  crops,  and  cotton. 

Manor  Series. — The  Manor  soils  are  characterized  by  their  yel- 
lowish-brown to  brown  surface  color  and  the  yellow  to  yellowish- 
red  or  dull  red  color  of  the  subsoils.  This  series  is  also  high  in  mica 
in  both  soils  and  the  subsoil.  They  are  derived  from  mica  and 
chlorite  schists.  Good  yields  of  corn,  wheat,  oats,  Irish  potatoes, 
and  hay  are  obtained. 

Penn  Series. — The  Penn  series  includes  Indian-red  soils  derived 
through  the  processes  of  weathering  from  red  sandstones  and  shales 
of  Triassic  age.  Detached  areas  of  these  rock  formations  occur  in 
shallow  basins  in  the  Piedmont  Plateau  from  the  vicinity  of  New 
York  to  South  Carolina.  Corn,  wheat,  oats,  potatoes,  grass,  apples, 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  81 

and  peaches  are  produced  in  the  northern  and  tobacco  and  cotton  in 
the  southern  states. 

York  Series. — The  types  included  in  the  York  series  are  pre- 
dominantly gray  to  light  gray  at  the  surface  and  have  yellow  sub- 
soils. They  are  derived  from  talcose  and  micaceous  schists  an"3 
imperfectly  crystalline  slates.  Crop  yields  are  usually  low  and  the 
soils  are  exceedingly  difficult  to  improve. 

II.    THE  APPALACHIAN  MOUNTAIN  AND  PLATEAU  PROVINCE 

This  province  embraces  three  subdivisions  of  the  Appalachian 
system,  which  extend  from  Xew  Jersey  and  northern  Pennsylvania 
to  central  Alabama.  They  are  as  follows:  (1)  The  Blue  Ridge 
region  on  the  east  and  southeast  side;  (2)  The  Cumberland- Alle- 
gheny plateau  on  the  west;  and  (3)  the  Appalachian  ridge  and 
valley  belt  between.  The  province  includes  two  subordinate  divi- 
sions, lying  outside  of  this  general  area:  (1)  the  Ouachita  and 
Boston  mountain  ridge  of  the  Ozark  uplift  west  of  the  Mississippi 
River,  and  (2)  the  area  of  Coal  Measure  rocks  in  western  Ken- 
tucky and  southern  Indiana.  The  Appalachian  constitutes  the 
greater  part  of  the  province  and  forms  a  broad  belt  approximately 
900  miles  long.  It  includes  the  mountains,  ridges,  and  valleys  of 
this  area.  This  province  is  about  200  miles  wide  in  Pennsylvania 
and  attains  a  maximum  breadth  of  about  270  miles  in  Virginia. 

Berks  Series. — The  soils  of  the  series  are  yellowish-brown  to 
brown  with  yellowish  subsoils.  The  soils  are  derived  from  the 
Hudson  River  shales,  which  are  yellow,  brown,  grayish,  and  olive- 
Colored.  They  occupy  rounded  ridges  and  hills  with  good  drainage. 
They  are  suited  to  corn,  oats,  wheat,  and  Irish  potatoes. 

Conasauga  Series. — The  Conasauga  scries  are  light  brown,  and 
the  subsoils  are  yellow  and  prevailingly  of  silty  clay  loam  to  silty 
clay  in  texture.  These  soils  are  developed  typically  in  flat  to  gently 
rolling  valley  lands.  They  are  derived  from  interbedded  shale,  lime- 
stone, and  fine-grained  sandstone.  Good  yields  of  cotton,  corn, 
wheat,  oats,  and  forage  crops  may  be  secured. 

De  Kalb  Series. — The  surface  soils  of  this  series  are  gray  to 
brown,  while  the  subsoils  are  commonly  some  shade  of  yellow.  The 
soils  are  derived  from  the  disintegration  of  sandstones  and  shales. 
The  surface  features  consist  of  gently  rolling  table  lands,  hills,  and 
mountains.  The  soils  are  generally  not  very  productive,  but  the 
stony  and  sandy  members  are  adapted  to  orchard  fruits,  while  the 
6 


82  SOIL  PHYSICS  AND  MANAGEMENT 

heavier  ones  produce  hay  and  pasture  grasses.  Sixteen  million  acres 
of  this  series  have  been  mapped. 

Fayetteville  Series. — This  series  consists  of  grayish  brown  to 
brown  soils  with  yellowish  brown  to  reddish  brown  subsoils.  The 
soils  are  formed  by  the  weathering  of  sandstones  and  shales  and  are 
found  throughout  a  large  part  of  western  and  northwestern  Arkan- 
sas and  eastern  Oklahoma.  They  are  moderately  fertile. 

Hanceville  Series. — The  Hanceville  series  has  a  light  brown  to 
reddish  brown  surface  and  a  red  subsoil.  The  topography  ranges 
from  rolling  to  steeply  rolling.  The  soils  are  derived  from  sand- 
stones and  shahs  and  are  moderately  productive. 

Meigs  Series. — This  series  is  variable  in  character  and  particu- 
larly in  color,  which  ranges  from  Indian  red  to  gray  or  pale  yellow. 
The  soils  are  derived  from,  red,  fine-grained  sandstones  and  shales 
and  from  grayish  sandstone  and  shales.  The  topography  is  steeply 
rolling.  The  soils  are  suited  to  grass  and  the  production  of  hay. 

Porters  Series. —  This  series  includes  the  residual  soils  of  the 
Appalachian  mountains  derived  from  igneous  and  metamorphic 
rocks.  They  occur  at  high  elevations.  The  soils  are  particularly 
adapted  to  fruit  culture. 

Talladega  Series. — The  soils  of  this  series  are  grayish  brown  to 
light  brown.  The  subsoils  are  red  and  have  a  greasy  feel.  The  soils 
are  derived  from  metamorphic  rocks,  principally  micaceous  schists. 
The  topography  is  strongly  rolling  to  mountainous.  They  give 
moderate  yields  of  corn,  forage  crops,  and  cotton. 

Upshur  Series. — In  the  Upshur  series  both  soils  and  subsoils 
are  Indian  red.  Some  types  have  the  grayish  to  grayish-red  color 
in  the  surface  soils.  They  are  derived  from  Indian-red  sandstones 
and  shales,  frequently  of  calcareous  nature.  They  occupy  rolling 
to  mountainous  regions.  They  are  generally  more  productive  than 
.the  De  Kalb  series. 

Westmoreland  Series. — This  series  is  marked  by  the  grayish 
brown  to  yellowish  brown  color  and  mellow  structure  of  the 
surface  soils  and  the  yellowish  brown  to  yellow  color  and  friable 
structure  of  the  subsoils.  The  soils  are  derived  from  shales  and 
sandstones,  with  interbedded  limestones  and  calcareous  shales.  The 
topography  ranges  from  gently  sloping  to  quite  rolling  or  steep 
lands.  These  soils  are  very  productive,  being  particularly  adapted 
to  corn,  oats,  wheat,  grass,  potatoes,  apples,  peaches,  plums,  cher- 
ries, berries,  and  vegetables. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  83 

III.    LIMESTONE  VALLEYS  AND  UPLANDS  PROVINCE 

This  province  includes  two  important  topographic  divisions — 
the  limestone  valleys  and  uplands.  The  limestone  valleys  are  most 
extensively  developed  within  the  Appalachian  Mountain  System, 
and  hesides  these  the  Central  Basin  of  Tennessee  and  the  bluegrass 
region  of  Kentucky. 

The  uplands  division  includes  a  large  area  extending  from 
Alabama  through  Tennessee  and  Kentucky  almost  to  the  Ohio 
River.  The  0/ark  region  of  southern  Missouri,  northern  Arkansas, 
northeastern  Oklahoma,  and  southeastern  Kansas  is  included. 

The  principal  soil  series  are  as  follows : 

Brooks  Series. — The  soils  are  grayish  brown  to  brown  with 
yellowish  brown  to  slightly  reddish  brown  clay  subsoils.  The  soils 
are  derived  from  pure  limestones,  with  an  occasional  admixture  of 
material  from  associated  sandstone  and  shales.  These  soils  have 
good  drainage.  Wheat,  corn,  oats  and  apples  do  well. 

Clarksville  Series. — The  soils  are  gray  and  the  subsoils  yellow 
arid  usually  silty  clay  in  texture  and  frequently  underlain  by  a 
reddish  substratum.  The  depth  to  red  material  varies  with  the 
topography,  being  deeper  on  the  more  level  areas.  The  soils  are 
derived  from  a  cherty  limestone  and  occur  over  both  level  and  un- 
dulating uplands  and  rough  and  hilly  country  with  steep  slopes. 
They  arc  adapted  to  tobacco,  grass,  small  grains,  corn,  strawberries 
and  cantaloupes.  Over  live  million  acres  have  been  mapped. 

Colbert  Series. — The  surface  soil  is  grayish  to  light  brown  and 
the  subsoil  yellow  and  frequently  plastic.  The  series  is  derived 
from  pure  limestone  or  a  limestone  mixed  with  sandstone.  The 
topography  is  flat  to  undulating  and  drainage  is  generally  poorly 
established.  With  proper  drainage  wheat,  oats,  corn,  and  forage 
crops  can  be  grown  with  good  results. 

Conestoga  Series. — These  soils  are  yellowish  brown  to  brown. 
The  subsoils  are  yellow  greenish,  occasionally  mottled  with  gray* 
and  have  a  greasy  feel.  These  soils  are  derived  from  schistose  lime- 
stone and  calcareous  shale  or  shaly  limestone.  They  are  adapted 
to  general  farm  crops. 

Decatur  Series. — The  soils  are  characterized  by  a  reddish 
brown  to  deep  red  color  and  subsoils  by  an  intensely  red  or  blood 
red  color.  They  are  derived  mainly  from  pure  limestone,  with  some 
traces  of  chert,  and  are  adapted  to  corn,  small  grains  and  forage 
crops.  They  occur  as  nearly  level  to  gently  rolling  valley  lands. 

Hagerstown  Series. — The  soils  of  this  scries  are  prevailingly 


84  SOIL  PHYSICS  AND  MANAGEMENT 

brown  in  color,  with  light  brown  to  reddish  brown  subsoils,  but 
never  so  distinctly  red  as  the  Decatur  series.  The  topography  is 
undulating  to  gently  rolling.  They  are  derived  from  limestone. 
The  soils  are  very  productive  and  well  adapted  to  corn,  small  grain, 
clover,  blue  grass,  timothy,  and  apples.  Three  million  acres  have 
been  mapped. 


IV.  THE  GLACIAL  AND  LOESSIAL  PROVINCE 

The  glacial  and  loessial  province  includes  that  part  of  the  United 
States  lying  east  of  the  Great  Plains  in  which  the  soils  are  derived 
from  ( 1 )  ice-laid  deposits  left  by  the  retreat  of  the  ice  at  the  close 
of  the  glacial  period,  (2)  water-laid  material  intimately  associated 
with  the  ice-laid  material,  deposited  during  the  advance  and  retreat 
of  the  ice  in  the  form  of  out- wash  plains,  and  (3)  silt  deposits  laid 
down  by  water  or  wind  during,  or  subsequent  to,  the  retreat  of  the 
ice.  The  ice-laid  deposits  are  found  north  of  an  irregular  line  run- 
ning from  Cincinnati  to  La  Crosse,  Wisconsin,  thence  southward 
to  Iowa  City,  Iowa,  continuing  in  a  westerly  direction  to  the  south- 
eastern corner  of  South  Dakota.  South  of  that  line  they  are  mainly 
loessial,  presumably  wind-laid  deposits.  The  two  tongues,  the  one 
running  down  the  Mississippi  and  the  other  southwestward  across 
Kansas  and  Oklahoma,  are  entirely  so. 

Bangor  Series. — This  series  is  characterized  by  grayish  to  yel- 
lowish brown  surface  soils,  with  subsoils  of  lighter  gray  and  yellow- 
ish brown.  All  of  the  types  are  stony  and  gravelly.  The  soils  are 
derived  from  glacial  till  containing  more  or  less  material  from  the 
local  serecitic  schist  rock.  The  topography  is  rolling  to  hilly.  With 
the  exception  of  the  stony  loam  and  shallow  phase  of  the  loam  the 
types  of  this  series  are  fair  general  farming  soil. 

Caribou  Series. — The  members  of  this  series  have  yellowish 
.brown  soils  which  usually  rest  upon  a  light  gray  lower  till.  The 
soil  material  is  derived  from  glacial  till  overlying  calcareous  shales 
or  shaly  limestone,  the  till  itself  being  derived  from  the  under- 
lying calcareous  formation,  having  been  transported  for  only  short 
distances.  The  soils  are  very  productive,  being  especially  adapted 
to  Irish  potatoes,  grain  and  peas. 

Carrington  Series. — These  soils  are  derived  through  weather- 
ing of  the  glacial  till  with  little  or  no  modification  from  loessial  de- 
posits. The  soils  are  generally  prairie,  black  in  color,  ranging  in 
some  cases  to  dark  brown.  The  subsoils  are  lighter  colored  gen- 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  85 

erally,  having  a  light  brown  or  yellowish  color.  The  topography 
is  gently  undulating  to  rolling.  Corn  and  wheat  are  the  principal 
crops  grown.  Nearly  four  million  acres  have  heen  mapped. 

Cazenovia  Series. — These  soils  are  brown  in  color  with  a  brown 
to  reddish  subsoil  resting  on  limestone  at  a  depth  of  about  3  feet. 
Fragments  of  limestone  and  red  sandstone  are  found  throughout 
the  soil  and  occasionally  large  boulders  are  scattered  over  the  sur- 
face. These  soils  are  derived  from  glacial  till  containing  consid- 
erable limestone  material.  The  principal  crops  are  grass,  alfalfa, 
corn,  wheat,  and  potatoes. 

^  Coloma  Series. —  The  soils  of  this  series  are  light  brown  to 
grayish  in  color  with  yellow  or  reddish  subsoils.  The  topography 
is  generally  rolling  to  rough  and  hilly,  representing  terminal  and 
ground  moraines.  The  series  is  formed  from  relatively  coarse 
glacial  material  modified  to  some  extent  by  the  action  of  the  wind 
and  water.  They  once  supported  extensive  pine  forests  and  are 
found  in  northern  Michigan,  Wisconsin,  and  Minnesota.  Nearly 
two  and  one-half  million  acres  have  been  mapped. 

Cossaymna  Series. — These  soils  are  brown  or  snuff  colored, 
with  subsoils  of  the  same  color,  but  of  a  lighter  shade.  Both  strata 
contain  considerable  quantities  of  shale  and  calcareous  sandstone 
fragments  with  a  small  percentage  of  foreign  boulders.  They  are 
derived  from  glacial  till  and  occupy  rolling  to  hilly  uplands.  The 
principal  crops  are  corn,  oats,  hay,  potatoes,  apples  and  other 
tree  fruits. 

Dutchess  Series. — The  Dutchess  soils  are  brown  to  light  brown 
with  bluish,  light  brown,  yellowish  or  reddish  brown  subsoils.  The 
soils  are  friable,  the  subsoils  being  somewhat  heavier  in  texture 
than  the  soil.  In  some  types  rounded  and  angular  gravel  occur  in 
both  soil  and  subsoil.  Those  are  rarely  of  limestone.  The  to- 
pography is  rolling  to  undulating  and  rough.  The  soils  are  adapted 
to  oats,  grass,  potatoes,  and  tree  fruits. 

Flushing  Series. — The  soils  are  brown  in  color  and  overlie  yel- 
lowish or  reddish  subsoils,  sometimes  micaceous  and  in  some  in- 
stances resting  on  crystalline  rock.  The  material  is  of  glacial  origin. 

Gloucester  Series. — The  soils  of  the  Gloucester  series  are  light 
brownish  or  often  grayish  at  the  immediate  surface  and  overlie  yel- 
low subsoils.  The  soils  are  derived  from  a  rather  local  glaciation 
of  crystalline  rocks  of  granites  aiid  gneiss.  The  drainage  is  fair 
to  good.  The  topography  ranges  from  gently  undulating  to  rolling 
or  hillv.  Scattered  rocks  and  boulders  of  large  size  occasionally 


86  SOIL  PHYSICS  AND  MANAGEMENT 

occur,  rendering  the  use  of  farm  machinery  somewhat  difficult. 
They  give  fair  yields  of  corn,  potatoes,  oats,  hay,  and  fruit. 

Holyoke  Series. — The  soils  are  brown  to  dark  yellow  in  color. 
The  subsoils  are  yellow  and  somewhat  heavier  than  the  soils.  They 
are  of  glacial  origin  and  derived  from  metamorphie,  diabase  and 
crystalline  rocks.  The  topography  is  rough  and  the  soils  are  mod- 
erately productive. 

I  Kewaunee  Series. — This  series  is  characterized  by  grayish  to 
reddish  brown  or  pinkish  soils  overlying  pinkish  red  silty  clay  and 
rather  calcareous  subsoils.  They  are  derived  from  till  and  contain 
more  or  less  angular  pebbles.  The  topography  varies  from  undu- 
lating to  hilly,  but  the  underdrainage  is  generally  poor. 

-'  Knox  Series. — These  soils  are  light  brown  and  are  derived  from 
loessial  or  other  wind  blown  deposits.  The  topography  is  gently 
undulating  to  rolling.  Grain  crops  constitute  the  chief  agricultural 
products.  About  three  million  acres  have  been  mapped. 

Lackawanna  Series. — These  soils  are  derived  from  glacial  drift 
that  forms  a  relatively  thin  mantle  overlying  the  red  shales  and 
limestones.  The  topography  is  slightly  rolling  to  hilly  and  moun- 
tainous. 

Lexington  Series. — Lexington  soils  are  gray  to  yellowish  gray 
in  color  and  mellow  in  structure.  The  subsoil  is  yellow  to  brown, 
with  a  tinge  of  red  in  places,  and  is  often  somewhat  heavier  than 
the  soil.  Drainage  is  good  and  the  topography  is  moderately  rolling 
to  hilly.  The  types  are  derived  from  loess  with  orange  sand  a  few 
feet  below  the  surface.  These  soils  are  adapted  to  corn,  cotton, 
forage  crops,  vegetables,  and  strawberries. 

Marion  Series. — These  soils  are  gray,  white  or  ash  colored. 
The  subsoils  are  white  at  the  top,  the  white  layer  varying  in  thick- 
ness from  2  to  12  inches  and  averaging  about  five  inches.  This 
layer  is  compact,  impervious,  whitish  silt  or  very  fine  sand,  often 
containing  iron  concretions  and  locally  known  as  "hard-pan."  Be- 
neath this  the  true  subsoil  is  a  gray,  light  yellow  to  reddish  yellow  or 
mottled  brownish  yellow,  hard,  impervious  clay  containing  occa- 
sional concretions  of  iron  and  lime.  The  topography  is  flat  to  un- 
dulating. Drainage  is  poor.  They  are  derived  from  modified  loess. 

Marshall  Series. — The  Marshall  series  includes  the  dark  col- 
ored upland  loessial  soils  which  predominate  in  the  great  prairie 
region  of  the  central  west.  The  surface  soils  have  a  dark  brown 
to. black  color.  The  topography  is  level  to  rolling  and  artificial 
drainage  is  usually  necessary  to  "secure  best  results.  They  aje  very 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  87 

productive   and    constitute   the   great   corn   soils   of   the   country. 
Nearly  four  million  acres  have  been  mapped. 

Memphis  Series. — The  Memphis  series  is  characterized  by  the 
light  brown  to  yellowish  brown  color  and  silty  texture  of  the  sur- 
face soils  and  by  the  slightly  lighter  colored  and  more  compact 
structure  of  the  subsoils.  They  occur  south  of  the  latitude  of  St. 
Louis  and  are  most  extensive  in  the  loessial  belt  following  the 
east  bank  of  the  Mississippi  river.  Erosion  has  been  active  and 
has  resulted  in  a  prevailingly  rolling  to  broken  topography.  They 
are  well  suited  to  corn,  oats,  peanuts,  forage  crops,  and  cotton.  The 
amount  mapped  is  2,000,000  acres. 

•  i  Miami  Series. — The  soils  are  brown,  light  brown  or  grayish 
and  are  underlain  by  yellowish  and  brown  heavier  textured  soils. 
Mottlings  of  brown  and  light  gray  are  present  in  the  subsoils.  Sur- 
face drainage  is  usually  good.  The  soils  in  the  main  are  derived 
from  the  weathering  of  glacial  till  composed  largely  of  ground-up 
limestone.  Dairying  is  an  important  industry  on  the  heavier  types. 
Nearly  four  million  acres  have  been  mapped. 

Mohawk  Series. — The  Mohawk  soils  consist  of  dark  colored 
glacial  material  derived  in  part  from  dark  colored  calcareous  shales 
and  limestones,  but  modified  by  admixture  of  glacial  till  from  other 
formations.  The  topography  is  rolling  to  hilly  and  they  are  con- 
sidered good  general  farming  soils. 

Ontario  Series. — These  soils  are  brown  to  chocolate  brown  in 
color,  the  subsoils  being  lighter  and  in  many  cases  grading  into 
yellow.  Both  soil  and  subsoil  usually  contain  scattered  fragments 
of  limestone  and  are  derived  from  glacial  till  of  the  drumlin  region 
of  New  York.  The  topography  is  undulating  to  hilly. 

Plymouth  Series. — These  soils  are  derived  from  moderately 
coarse  glacial  material  largely  from  granites.  The  series  includes 
the  morainal  and  till  deposits  found  in  southeastern  Xcw  England 
and  on  Tx>ng  Island.  The  surface  soil  is  shallow  and  brown,  under- 
lain by  a  pale  yellow  subsoil. 

Putnam  Series. — This  series  includes  dark  gray  to  black  soils 
overlying  impervious  drab  or  brown  subsoils  of  fine  texture  and  close 
structure.  One  of  its  principal  characteristics  is  the  presence  of  a 
whitish  silty  layer  between  the  soil  and  the  subsoil.  The  soils 
occupy  level  to  gently  undulating  prairies  and  are  derived  from 
loessial  deposits.  Drainage  is  poor  because  of  the  dense  compact 
structure  of  the  subsoil.  They  are  confined  to  Missouri. 

Richland  Series. — The  Hichland  series  is  characterized  by  a 


88  SOIL  PHYSICS  AND  MANAGEMENT 

light  brown  to  yellowish  brown  color  and  silty  texture  of  the  sur- 
face soils  and  the  somewhat  lighter  color  and  more  compact  struc- 
ture of  the  subsoils.  These  soils  are  derived  from  the  loess  and 
occur  in  association  with  the  Memphis  soils.  The  topography  is 
smooth,  flat  to  undulating.  Cotton,  corn,  peanuts,  oats,  forage 
crops,  clover,  cabbage  and  Irish  potatoes  give  very  good  results. 

Shelby  Series. — The  soils  of  this  series  are  yellowish  gray  or 
yellowish  brown  to  brown  in  color.  The  subsoils  are  yellow  or  red- 
dish yellow  or  light  brown  tenacious  sandy  clays.  The  subsoils 
are  derived  from  the  Kansas  drift  and  occupy  steep  stream  slopes. 
They  were  originally  covered  with  white  oak,  some  hickory,  red  oak 
and  elm. 

Trumbull  Series. — The  Trumbull  series  consists  of  gray  sur- 
face soils,  underlain  by  light  gray  or  gray  mottled  with  yellow  sub- 
soils, which  at  an  average  depth  of  about  18  inches  becomes  a  mot- 
tled gray  and  yellow.  The  soils  are  without  limestone  to  a  depth  of 
3  feet.  They  are  derived  from  shales  and  sandstones.  Corn,  oats, 
wheat  and  hay  are  the  principal  crops  grown. 

Union  Series. — The  soils  of  this  series  are  characteristically 
brown  to  grayish  brown  in  color,  of  silty  texture  and  friable  struc- 
ture, with  yellowish  brown  silty  and  moderately  friable  subsoils.  It 
is  probably  partly  of  loessial  origin.  The  topography  is  gently  roll- 
ing to  hilly. 

Volusia  Series. — The  soils  of  this  series  are  the  result  of  feeble 
glaciation  of  the  shales  and  sandstones  of  the  Devonian  and  the 
Upper  Carboniferous  rocks  of  eastern  Ohio,  southern  New  York, 
and  northern  Pennsylvania.  The  underlying  shales  and  sandstones 
have  given  rise  to  a  large  proportion  of  the  soil  material,  which  has 
been  modified  in  varying  degrees  by  other  glacial  material.  The 
series  is  well  adapted  to  the  production  of  timothy  and  small  grains. 
Wheat  and  corn  give  good  yields  at  lower  elevations.  Over  six 
million  acres  have  been  mapped. 

Williams  Series. — The  soils  of  this  series  are  of  a  dark  gray  to 
brown  or  dark  brown  color,  generally  underlain  at  8  to  12 
inches  by  lighter  brown  subsoils  which  grade  quickly  into 
light  gray,  ashen  or  putty  colored  subsoils  of  calcareous  character 
and  usually  of  fine  and  often  of  silty  texture.  Tl\ey  are  derived 
from  glacial  material  and  contain  gravel  and  boulders.  The  sur- 
face is  treeless  and  varies  from  level  prairies  to  rough  hilly  terminal, 
morainic  belts.  Nearly  14,500,000  acres  have  been  mapped.  - 

Wooster  Series. — The  Wooster  series  includes  the  yellowish 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  89 

brown  glacial  shale  and  sandstone  soils,  having  unmottled  brownish 
gray  subsoils.  When  dry  the  surface  in  plowed  fields  is  a  light  gray, 
but  underneath  the  surface  or  when  moist  the  soils  are  always 
yellowish  or  light  brown.  The  subsoils  are  of  a  brownish  yellow 
with  just  a  slight  tinge  of  red.  They  are  derived  from  shales  and 
sandstones.  Wheat,  corn,  oats,  hay,  and  potatoes  are  the  principal 
crops  grown. 

V.  GLACIAL  LAKE  AND  RIVER  TERRACE  PROVINCE 

The  Glacial  Ijake  and  River  Terrace  Province  embraces  two 
classes  of  deposits.  The  first  class  includes  deposits  in  the  basins 
of  lakes  formed  by  the  advance  and  retreat  of  ice  during  the  Glacial 
period.  These  were  temporary  lakes  which  took  form  during  the 
period  of  the  retreat  of  the  ice  or  lakes  that  were  formed  then  but 
have  since  been  drained  through  the  operation  of  natural  drainage 
forces. 

The  second  class  of  deposits  consists  of  those  left  within  the 
glaciated  area  by  the  streams  that  flowed  from  the  ice  during  the 
Glacial  period.  These  streams  were  more  abundantly  supplied  with 
water  from  the  melting  ice  than  at  present  from  the  normal  rainfall 
of  the  glacial  region.  They  also  carried  large  quantities  of  gravel, 
sand  and  finer  material  which  were  deposited  in  the  valleys,  form- 
ing new  slopes  whose  grades  were  determined  by  the  load  and  cur- 
rent of  the  streams.  Since  the  reduction  of  tbe  volumes  of  the 
streams  new  valleys  have  been  formed  through  the  old  material. 

The  province  consists  of  a  large  number  of  isolated  areas,  many 
of  them  a  square  mile  or  less  in  extent.  The  river  terraces  are 
developed  as  small,  irregular  areas  or  strips  along  the  streams.  The 
larger  areas  lie  within  the  former  basins  of  the  lakes.  The  principal 
series  are  as  follows: 

Chenango  Series. — This  series  consists  of  yellowish  to  light 
brown  surface  soils  and  brown  to  yollow  subsoils.  The  surface  soils 
vary  in  texture.  The  subsoils  pass  into  stratified  gravel  or  coarse 
sand  at  three  feet  or  more  in  depth  The  series  includes  terrace 
soils  occurring  along  streams.  The  soils  are  of  high  agricultural 
value,  and  are  well  adapted  to  corn,  alfalfa,  potatoes,  and  truck 
crops. 

•4  Clyde  Series. — This  series  is  characterized  by  dark  brown  to 
black  surface  soils  and  gray,  drab  or  mottled  gray  and  yel- 
lowish subsoils  derived  through  deposition  or  reworking  of  the  soil 


90  SOIL  PHYSICS  AND  MANAGEMENT 

material  in  glacial  lakes  or  ponds.  The  soils  of  this  series  grade 
into  muck  and  peat.  The  topography  is  level  and  the  soil  is  nat- 
urally poorly  drained.  They  are  highly  productive  and  valuable 
for  corn,  grass,  sugar  beets,  cabbage,  and  onions.  About  1,500,000 
acres  have  been  mapped. 

Dunkirk  Series. — The  soils  are  derived  from  the  weathering  of 
glacial  lake  deposits  and  include  the  lighter  colored  soils  formed 
from  such  material.  The  surface  soils  range  from  brown  to  gray 
in  color  and  the  subsoils  from  brown  to  yellow  or  gray  with  or 
without  mottling.  The  topography  varies  from  smooth  to  rough. 
An  area  of  almost  two  million  acres  has  been  mapped. 

Fargo  Series. — This  series  occurs  principally  in  the  old  glacial 
Lake  Agassiz,  in  the  Red  River  Valley,  and  in  other  old  glacial  lake 
beds  in  the  same  region.  They  are  very  black  in  color,  containing 
a  very  large  per  cent  of  organic  matter,  in  some  cases  enough  to 
make  them  slightly  mucky.  The  subsoil  contains  a  large  amount  of 
lime.  The  topography  is  level.  The  area  mapped  is  nearly  3,000,- 
000  acres. 

Fox  Series. — These  are  gray  to  brown  and  of  level  or  slightly 
undulating  topography.  The  material  was  laid  down  as  outwash 
plains  or  terraces  along  streams  within  the  glacial  area. 

Manchester  Series. — The  soils  of  the  Manchester  series  are 
generally  rather  sandy  in  texture  and  the  surface  soils  are  red  or 
brown  in  color.  The  subsoils  are  red  or  reddish  and  in  the  lower 
part  grade  into  the  glacial  till.  They  are  formed  from  old  alluvial 
or  lacustrine  sediments  disposed  as  terraces  in  the  Connecticut 
Valley.  They  are  adapted  to  fruit,  early  truck,  grains,  and  tobacco. 

Merrimac  Series. — The  surface  soils  of  the  Merrimac  series 
are  brown  to  light  brown  in  color  and  usually  underlain  by  yellowish 
sand  and  gravel.  They  constitute  the  glacial  terraces  found  along 
nearly  all  streams  in  Xew  England.  The  material  consists  princi- 
pally of  crystalline  rocks  which  were  ground  up  by  the  ice  and 
reworked  by  water. 

Orono  Series. — The  surface  soils  are  light  hrown  and  gray  and 
the  subsoils  are  gray.  The  heavier  types  occur  as  estuarine 
and  glacial  lake  plains  or  outwash  plains.  The  lighter  types  are 
derived  from  esker  and  glacial-delta  material.  The  adaptation  to 
crops  varies  with  the  texture  and  drainage.  The  heavier  soils  are 
best  suited  to  grass  and  grains,  the  intermediate,  to  general  farming, 
and  the  light  sandy  ones  to  truck  crops. 

.  Plainfield  Series. — The  surface  soils  of  the  Plainfield  series 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  91 

range  in  color  from  brown  to  grayish  yellow,  while  the  subsoils  are 
usually  yellow  to  pale  yellow.  The  series  is  developed  in  the  deep 
drift-covered  areas  of  Wisconsin,  Michigan,  and  Minnesota,  and 
are  derived  from  sandy  and  gravelly  glacial  debris  washed  out  from 
the  fronts  of  the  glaciers.  The  type  is  also  found  in  deep  filled-in 
valleys.  The  greater  part  of  the  material  of  the  series  has  been 
considerably  assorted  by  glacial  waters  and  consists  mainly  of  sand 
and  gravel. 

Sioux  Series. — This  series  occurs  in  the  glaciated  region  of 
the  central  and  northwestern  states  and  comprises  the  dark  brown 
to  black  terrace  soils  and  with  a  bed  of  gravel  within  three  feet  of 
the  surface.  It  occurs  as  narrow  areas  along  streams  instead  of 
bnjad  outwash  plains. 

~  Superior  Series. — The  surface  soils  are  gray,  brown  or  reddish, 
with  pinkish  red  to  light  chocolate  red  rather  dense  clay  subsoils. 
The  series  comprises  a  group  of  glacial-lake  soils  developed 
mostly  along  the  margin  of  Lake  Superior.  The  topography  is 
usually  level  to  slightly  undulating.  The  series  is  well  adapted  to 
the  production  of  grasses,  grains  and  the  general  farm  crops. 

Vergennes  Series. — This  series  is  marked  by  brown,  yellowish 
or  gray  soils  underlain  at  varying  depths  by  drab  to  blue  or  light 
gray  clay  subsoils,  often  calcareous.  Jt  consists  of  deep-water  sedi- 
ments known  as  the  Champlain  clays  deposited  in  post-glacial  times 
over  glacial  drift  during  a  period  of  submergence.  Since  the  uplift 
these  clays  have  been  more  or  less  modified  by  the  stream  action 
and  colluvial  wash  from  the  surrounding  highlands.  The  surface 
is  level  to  gently  rolling. 

^  Waukesha  Series. — The  Waukesha  series  is  characterixed  In- 
dark  brown  to  black  surface  soils  underlain  by  yellow  subsoils  in 
which  fine  gravel  is  usually  present.  They  are  derived  from  water- 
assorted  glacial  debris  deposited  in  broad  filled-in  valleys  or  as  out- 
wash  plains  and  terraces,  and  are  sandy  and  gravelly  in  general 
character.  They  are  more  productive  than  1'lainlield  soils. 

VI.    ATLANTIC    AND    (JTLK    COASTAL    PLAIN'S    IMiOVI  NCIC 

The  Atlantic  and  (Julf  Coastal  Plains  Province  constitutes  one 
of  the  most  important  physiographic  divisions  of  the  Tinted  States. 
This  province  comprises  approximately  :}(>.">, 000  square  miles  of  the 
predominantly  flat  to  smoothly  rolling  region  bordering  the  Atlantic 
Ocean  and  extending  from  the  northern  end  of  Long  Island  in  New 


92  SOIL  PHYSICS  AND  MANAGEMENT 

York  to  the  southern  extremity  of  Florida  and  along  the  Gulf  of 
Mexico  to  the  mouth  of  the  liio  Grande.  There  is  a  broad  gap  in 
the  Gulf  Plain  represented  hy  the  Mississippi  bottoms  and  the  belt 
of  loessial  soils  adjoining  the  bottoms  on  the  east. 

In  its  general  aspect,  the  Atlantic  and  Gulf  Coastal  Plains 
Province  consists  of  a  broad  plain  which  rises  gradually  either  from 
sea  level  or  low  bluffs  along  the  coast  to  the  border  of  the  high 
inland  regions  of  different  topographic  forms.  The  inner  boundary, 
representing  the  highest  part  of  the  main  province,  varies  from 
200  to  500  or  600  feet  above  sea  level.  This  region,  although 
formerly  a  plain  changing  to  a  gradual  slope  from  the  sea  inland, 
has  been  eroded  since  its  uplift  above  sea  level  to  its  present  vary- 
ing topographic  features  of  low  to  moderate  relief  as  compared  with 
the  much  more  uneven  surface  of  the  Appalachian  and  Piedmont 
regions.  The  most  important  series  are  as  follows: 

Acadia  Series. — The  surface  soils  are  light  gray  or  white,  with 
mottled  gray  and  yellow,  or  gray,  yellow  and  red  friable  subsoils, 
carrying  lime  nodules  and  iron  concretions.  They  are  derived 
mainly  from  reworked  loessial  material.  The  surface  is  gently 
rolling,  and  the  series  is  now  timbered  with  pine,  oak,  gum,  hickory 
and  some  cypress.  It  is  adapted  to  the  production  of  corn,  cotton, 
peas,  and  oats. 

Brennan  Series. — This  series  consists  of  gray  calcareous  soils 
containing  a  small  amount  of  humus  and  a  large  amount  of  lime. 
They  have  been  derived  from  Pleistocene  deposits  in  broad  valleys. 
They  are  of  higher  agricultural  value  than  the  former. 

Caddo  Series. — The  soils  are  gray  to  yellow  in  color.  The  sub- 
soils are  mottled  gray  and  yellow,  or  gray,  yellow  and  red,  and  of  a 
rather  stiff  structure.  In  some  places  the  subsoil  has  a  pronounced 
grayish  color,  while  in  others  it  is  a  mottled  yellow  and  gray.  Low 
sandy  mounds  or  hummocks  are  a  feature  of  the  series.  Cotton 
and  corn  are  the  principal  crops.  These  soils  are  most  'extensively 
developed  in  northwestern  Louisiana  and  northeastern  Texas  and 
are  derived  from  reworked  loessial  material. 

Coxville  Series. — The  series  comprises  dark  gray  to  nearly 
black  soils  derived  from  the  quiet  or  deep-water  deposits'  of  the 
Columbia  formation.  The  subsoils  range  from  a  moderately  mellow 
friable  clay  in  the  upper  portion  to  yellowish  plastic  compact  clay 
mottled  with  drab  and  bright  red  in  the  lower  portion.  The 
topography  is  prevailingly  flat.  They  are  well  adapted  to  cotton, 
corn,  oats,  and  certain  varieties  of  strawberries. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  93 

Crowley  Series. — The  soils  range  from  ashy  gray  to  light 
brown  in  color,  with  mottled  brown,  yellow  and  red,  to  almost  uni- 
formly yellow  clay  subsoils.  Lime  and  iron  concretions  are  present 
in  the  subsoil,  which  is  quite  impervious  to  water.  This  feature 
favors  the  production  of  rice.  The  topography  is  flat.  They  are 
typical  prairie  soils  of  Louisiana  and  Arkansas  formed  or  reworked 
loessial  material. 

Durant  Series. — The  series  consists  of  dark  gray  to  dark  brown 
surface  soils,  with  yellow  to  dark  brown  subsoils.  They  are  derived 
from  soft  sandstone  and  calcareous  marl.  The  soils  are  productive, 
giving  fair  yields  of  general  farm  crops. 

Duval  Series. — The  soils  are  marked  by  their  bright  red  color 
and  rather  low  lime  content.  They  are  derived  from  fluvial  de- 
posits of  red  sands  and  sandy  clays.  Three  and  one-half  million 
acres  have  been  mapped. 

Edna  Series. — The  soils  of  this  series  are  gray  to  dark  gray. 
The  subsoils  consist  of  gray  or  mottled  gray  and  yellow,  heavy,  im- 
pervious clay.  The  topography  is  level  to  gently  undulating.  They 
are  derived  from  the  weathering  of  noncalcareous  marine  deposits. 
The  supply  of  organic  matter  is  low.  They  are  not  very  productive, 
but  cotton,  corn  and  general  farm  crops  are  grown  to  some  extent. 
The  area  mapped  comprises  1,500,000  acres. 

Elkton  Series. — The  soils  are  light  gray  to  white  and  the  sub- 
soils are  mottled  whitish  gray  and  yellow.  U ravel  or  coarse  sand 
usually  saturated  with  water  is  found  at  a  depth  of  2VL>  to  3  feet. 
They  are  of  rather  low  agricultural  value. 

Goliad  Series. — These  soils  are  prevailingly  dark  gray  to  black 
with  reddish  brown  to  red  sandy  loam  or  sandy  clay  subsoils,  in  the 
lower  portions  of  which  a  white,  soft,  calcareous  substratum  is  en- 
countered. The  soil  material  consists  of  weathered  marine  deposits. 
They  are  fairly  productive. 

Greenville  Series. — These  soils  are  reddish  brown  to  dark  rod 
and  generally  loamy.  THe  subsoils  consist  of  red  friable  sandy  clay. 
The  types  occupy  level  to  gently  rolling  areas  in  the  Coastal  plains 
uplands.  They  are  well  adapted  to  cotton,  corn,  forage  crops  and 
oats. 

Houston  Series. — The  soils  are  black  and  high  in  lime,  espe- 
cially the  subsoils,  which  in  some  of  the  types  consist  of  white 
chalky  limestone.  The  members  of  the  series  occur  principally  in 
the  black  calcareous  prairie  regions  of  Alabama,  Mississippi  and 
Texas.  The  soils  have  been  derived  from  the  weathering  of  cal- 


94  SOIL  PHYSICS  AND  MANAGEMENT 

careous  clays,  chalk  beds  and  rotten  limestone,  of  Cretaceous  age. 
The  soils  of  this  series  are  very  productive  and  are  devoted  chiefly 
to  cotton  and  corn,  but  alfalfa  will  grow  on  some  of  the  types.  The 
area  mapped  comprises  6,300,000  acres. 

Lake  Charles  Series. — The  soils  of  this  series  are  gray  to 
black  in  color,  with  mottled  yellow  and  red  subsoils  carrying  lime 
and  iron  concretions.  The  surface  is  marked  by  low  sandy  mounds 
or  hummocks.  The  subsoil  is  quite  resistant  to  the  movements  of 
moistures,  and  drainage  is  poorly  established.  The  soils  are  best 
suited  to  sugar  cane  and  grass.  The  series  occurs  on  both  prairie 
and  tree-covered  areas  and  consists  mainly  of  reworked  loessial 
material.  The  sand  mounds  are  inclined  to  be  drouthy.  Some 
rice  is  grown. 

Leonardtown  Series. — The  soils  of  this  series  are  gray  to  pale 
yellow  in  color.  The  subsoils  are  mottled  gray,  yellow  and  red  and 
ordinarily  carry  clay  lenses  and  pockets  of  sand.  They  are  gently 
rolling  to  rolling.  They  are  best  suited  to  general  farm  crops. 

Lufkin  Series. — The  surface  soils  are  light  gray  and  underlain 
by  impervious,  plastic  and  gray  to  mottled  gray  and  yellow  sub- 
soils. The  difference  in  texture  between  the  surface  soil  and  sub- 
soil in  the  case  of  the  sandy  members  is  very  marked.  The  to- 
pography is  flat  and  drainage  is  poor.  The  soils  are  locally  known 
as  "  flatwoods"  land.  The  timber  growth  consists  largely  of  scrubby 
oak  and  post  oak.  About  two  million  acres  have  been  mapped. 

Maverick  Series. — The  soils  are  light  gray  to  brownish  in 
color  and  the  subsoils  yellowish  brown  to  drab  and  of  heavier  tex- 
ture. They  are  formed  by  the  mixing  of  limestone  and  sandstone 
with  calcareous  clays. 

Monroe  Series. — These  soils  are  gray  to  brown,  with  mottled 
yellow  and  red  friable  structure  of  the  subsoils.  They  occupy  nearly 
level  to  rolling  uplands  throughout  the  Atlantic  and  Gulf  Coastal 
Plains  and  have  been  derived  mainly  from  the  Piedmont-Appa- 
lachian material.  The  soils  are  usually  deficient  in  organic  matter. 
They  are  variously  adapted  to  early,  medium  and  late  truck  crops. 
The  area  mapped  comprises  thirteen  and  one-half  million  acres. 

Nueces  Series. — The  soils  and  subsoils  of  this  series  'are  gray 
and  are  underlain  by  a  stratum  of  stiff,  mottled,  grayish  clay.  The 
soils  are  derived  from  wind-blown  material  originally  from  the 
residual  prairies,  which  has  drifted  inland  from  the  coast.  The 
surface  is  prevailing  flat,  with  a  few  dunes.  They  are  poor  agri- 
culturally. The  soils  are  devoted  to  corn,  truck  crops,  and  pasture. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  95 

Oktibbeha  Series. — These  soils  are  prevailingly  dull  brown 
to  yellowish  brown.  The  subsoils  are  composed  of  somewhat  mot- 
tled yellow,  gray  and  red,  rather  plastie,  silty  clay.  They  are  under- 
lain by  soft  rotten  limestone.  The  topography  is  Hat  to  gently 
sloping.  They  are  locally  known  as  "  post  oak  lands  ''  or  "post 
oak  prairie  lands."  When  properly  bandied  they  produce  good 
crops  of  cotton,  corn,  Johnson  grass,  lespede/.a,  bur  clover,  and  a 
numl>er  of  other  crops. 

Orangeburg  Series. — The  soils  of  this  series  are  marked  by 
their  gray  to  reddish  brown  color  and  open  structure.  The  subsoils 
consist  of  friable  sandy  clay.  They  are  confined  to  the  uplands  of 
the  Atlantic  and  (iulf  Coastal  Plains,  being  most  extensively  de- 
veloped in  a  belt  extending  from  southern  Xorth  Carolina  to  cen- 
tral Texas.  This  is  a  very  valuable  series,  its  heavier  memlx?rs  being 
adapted  to  corn,  cotton,  cowpeas,  peanuts,  potatoes,  and  cigar  leaf 
tobacco.  Xearly  five  million  acres  have  been  mapped. 

Portsmouth  Series. — These  soils  are  dark  gray  to  black  and 
are  high  in  organic  matter.  The  subsoils  are  light  gray  to  mottled 
gray  and  yellow  and  the  heavier  types  are  always  plastic.  These 
soils  are  developed  in  flat  to  slightly  depressed,  poorly  drained  situa- 
tions and  require  drainage  before  they  can  be  used  for  agriculture. 
They  are  adapted  to  corn,  strawberries  and  truck  crops  such  as 
cabbage,  onions  and  celery.  Altogether  2,410,000  acres  have  been 
mapped. 

Ruston  Series. — The  soils  are  gray  to  grayish  brown,  and  are 
underlain  by  reddish  yellow  to  yellowish  red  or  dull  red  moderately 
friable  subsoils,  prevailingly  of  sandy  clay.  They  are  slightly  lower 
in  productiveness  than  Orangeburg. 

San  Antonio  Series. — These  soils  are  brown  to  chocolate  brown 
in  color  and  have  brownish  red  calcareous  subsoils.  Thev  are  de- 
veloped in  the  semi-arid  regions  of  southern  Texas.  Thev  are  de- 
rived from  calcareous  material  of  sedimentary  origin.  I'mler  irri- 
gation they  give  excellent  yields  of  a  number  of  crops  such  as  cotton, 
corn,  sorghum,  vegetables,  and  alfalfa. 

Sassafras  Series. — These  soils  arc  distinguished  by-tbeir  yel- 
lowish brown  to  brown  color  and  mellow  structure.  The  subsoils  arc 
reddish  yellow  and  friable  in  structure,  resting  upon  beds  of  graxel 
or  sand  varying  from  "2\ o  to  .r>  feet  in  thickness.  They  are  developed 
along  flat  marine  or  estuarine  terraces  from  10  to  2.">0  feet  above 
sea  level.  They  include  some  of  the  most  productive  soils  of  the 
Atlantic  seaboard.  Excellent  crops  of  wheat,  corn,  clover,  potatoes, 


96  SOIL  PHYSICS  AND  MANAGEMENT 

melons,  berries  and  vegetables  are  secured.  The  area  mapped  is 
1,717,000  acres. 

Scranton  Series. — These  soils  are  dark  gray  to  black,  with 
yellow  friable  subsoils.  The  topography  is  flat  arid  the  soils  are 
generally  in  need  of  better  drainage.  They  are  well  suited  to  corn, 
oats,  forage  crops  and  a  number  of  vegetables. 

Susquehanna  Series. — These  are  gray  to  reddish  gray  in  color 
and  are  underlain  by  mottled  red  and  gray  or  red,  gray  and  yellow 
plastic  heavy  clay  subsoils.  Red  is  always  the  predominating  color 
in  subsoils,  the  other  colors  appearing  as  mottlings.  The  soils 
are  developed  in  the  higher  portions  of  the  Coastal  Plain  from 
Chesapeake  Bay  to  Central  Texas.  The  heavier  members  are 
heavy 'to  handle  on  account  of  the  intractable  subsoil.  Corn  and 
oats  are  grown  extensively  in  the  northern,  wtih  cotton  in  southern 
states.  More  than  2,800,000  acres  have  been  mapped. 

Tifton  Series. — The  soils  are  gray  to  grayish  brown  in  color 
and  are  underlain  by  bright  yellow,  friable,  sandy  clay  subsoils. 
Small  iron  concretions  occur  on  the  surface  and  throughout  the 
soil  section.  Their  presence  gives  rise  to  the  local  name  of  "  pimply 
or  pebbly  land."  They  are  considered  very  valuable  and  are  adapted 
to  cotton,  sugar  -cane,  corn,  cowpeas,  velvet  beans,  oats,  rye,  sweet 
and  Irish  potatoes,  pecans,  figs,  plums,  and  vegetables. 

Victoria  Series. — This  series  consists  of  brown  to  black  soils 
with  gray  to  whitish,  calcareous  subsoils,  derived  from  the  Pleisto- 
cene deposits  of  the  Gulf  Coastal  Plains.  The  topography  is  rolling. 
Over  four  million  acres  have  been  mapped. 

Webb  Series. — The  soils  of  this  series  are  brown  to  reddish 
brown  with  reddish  brown  to  red  subsoil.  They  are  found  in  the 
semi-arid  areas  of  the  Coastal  Plains  of  Texas.  They  are  culti- 
vated to  some  extent.  Most  types  are  covered  with  thick  growth  of 
mesquite. 

Wilson  Series. — The  series  embraces  dark  gray  to  black  soils, 
with  mottled  gray  and  drab  to  black  subsoils,  usually  of  stiff, 
heavy  clay.  They  are  typically  developed  in  the  mixed  prairie  and 
timbered  regions  of  Texas  and  apparently  hold  a  position  inter- 
mediate between  Houston  and  Lufkin  series.  Red  is  practically 
absent.  The  surface  is  frequently  flat  so  that  water  stands  after 
heavy  rains.  The  heavier  members  dry  out  and  bake  quickly.  Cot- 
ton and  corn  are  the  principal  crops. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  97 

VII.  RIVER  FLOOD   PLAINS  PROVINCE 

The  soils  of  this  province  occupy  the  first  bottoms  and  adjoin- 
ing terraces  of  streams  throughout  that  section  lying  east  of  the 
Great  Plains  region.  Some  areas  of  flood  plains  soil  cover  the  bot- 
toms and  terraces  of  valleys  which  have  been  abandoned  by  their 
main  streams. 

These  soils  occur  in  continuous  and  interrupted  strips  along 
the  banks  of  streams.  They  vary  from  narrow  strips  a  few  rods 
wide  along  the  minor  drainage  courses  and  those  streams  which 
pass  through  gorge-like  valleys  to  broad  bottoms  several  miles  in 
width.  The  broadest  strip  of  strictly  alluvial  land  is  along  the 
Mississippi  Kiver,  where,  at  its  confluence  with  the  Arkansas,  it  is 
75  to  100  miles. 

The  soils  of  this  province  include  two  topographic  divisions: 
(1)  The  first  bottoms  or  present  flood  plains,  and  (2)  the  terraces 
or  old  flood  plains.  The  material  composing  these  soils  is  derived 
fiom  very  widely  distributed  sources  and  from  every  species  of 
rock.  The  principal  series  are  as  follows: 

Bibb  Series. — This  series  is  marked  by  light-colored  to  white 
compact  surface  soils  and  by  compact  plastic  and  white  or  mottled 
white  and  yellowish  subsoils.  The  material  is  derived  mainly  from 
Coastal  Plains  soils.  They  are  best  suited  to  grass  and  pastures 
under  present  conditions. 

Blanco  Series. — These  have  gray  to  light  brown  soils  and 
brownish  subsoils  which  in  the  lower  portions  change  to  plastic 
heavy  materials  of  a  decidedly  brown  color.  The  soil  and  subsoil 
are  calcareous.  These  soils  occupy  terraces  mainly  above  overflow. 
Soils  are  well  adapted  to  cotton,  corn,  Irish  potatoes,  and  alfalfa. 

Cahaba  Series. — The  .surface  soils  are  brown  to  reddish  brown 
and  the  subsoils  are  yellowish  red  to  reddish  brown.  They  are  ter- 
races principally  above  overflow.  These  soils  are  well  suited  to  cot- 
ton, corn,  oats,  and  forage  crops. 

Cameron  Series. — These  are  soils  of  dark  brown  to  black  color 
and  tenacious  character  and  highly  calcareous  subsoil.  The  series 
occupies  broad,  shallow  basins,  occurring  typically  between  river 
channels,  and  in  general  is  ]x>orly  drained.  The  lower  ]x>rtions  re- 
main flooded  during  the  greater  part  of  the  year.  Alkali  is  fre- 
quently present,  in  the  lower  depression.  fJood  crops  of  corn,  sugar 
cane,  cotton,  and  vegetables  are  successfully  grown. 

Congaree  Series. — The  soils  and  subsoils  of  this  series  are 
brown  to  reddish  brown,  there  being  comparatively  little  change  in 
7 


98  SOIL  PHYSICS  AND  MANAGEMENT 

texture,  structure  and  color  from  the  surface  downward.  They 
occur  as  first  bottom  of  the  Piedmont  region  and  in  the  Coastal 
Plain.  Soils  are  productive,  yielding  corn,  cotton,  cane,  oats  and 
forage  crops. 

Frio  Series. — These  consist  of  dark-colored  soils  which  have 
been  brought  down  from  the  Edwards  Plateau  and  deposited  in 
terraces  along  the  larger  streams.  They  are  excellent  agricul- 
tural soils. 

Genesee  Series. —  The  Genesee  series  consists  of  dark  brown  to 
grayish  brown  alluvial  sediment  deposited  along  the  major  streams 
and  their  tributaries  throughout  the  northeastern  glaciated  region. 
They  are  subject  to  overflow.  Good  soils  for  corn,  oats,  sugar  beets, 
potatoes,  cabbages,  and  grass. 

Holston  Series. — These  consist  of  yellowish  brown  to  brown 
surface  soils  and  yellow  subsoils.  It  is  developed  in  old  alluvial 
terraces,  sometimes  standing  200  feet  or  more  above  the  first  bot- 
tom of  streams.  The  material  is  derived  principally  from  sand- 
stone and  shale.  The  soils  give  fair  to  good  crops  of  corn,  wheat, 
oats,  grass,  clover,  and  forage  crops. 

Huntington  Series. — These  are  light  brown  to  brown  and  the 
subsoils  yellow  to  light  brown.  Frequently  there  is  little  change  in 
the  color  or  character  of  the  material.  They  occur  in  the  limestone 
and  Appalachian  Mountain  regions  as  first  bottoms.  They  are  ex- 
cellent soils  and  well  adapted  to  corn,  oats,  grass  and  forage  crops 
under  proper  climatic  conditions.  More  than  1,237,000  acres  have 
been  mapped. 

Kalmia  Series. — The  surface  soils  are  gray  to  grayish  yellow. 
The  subsoils  are  mottled  gray  and  yellow.  The  series  is  found  along 
streams  of  the  Coastal  Plain  on  terraces  above  overflow.  The  sur- 
face is  flat.  When  properly  drained  the  soils  are  suited  to  corn, 
cotton,  sugar  cane,  and  forage  crops. 

Laredo  Series. — This  series  consists  of  gray  to  light  brown, 
calcareous  soils  with  gray,  calcareous  subsoils.  They  occur"  as  ter- 
races along  streams  in  south  Texas,  and  are  quite  valuable  when 
irrigated. 

Lintonia  Series. — The  surface  soils  of  this  series  are  light 
brown  or  yellowish  brown  and  of  silty  texture.  The  subsoils  are  of 
slightly  lighter  color.  They  occupy  stream  terraces  and  alluvial 
land.  Grass,  forage  crops,  corn,  oats,  Irish  potatoes,  peanuts,  cab- 
bage, and  vegetables  are  grown. 

Miller  Series. — These  soils  are  of  chocolate  brown  to  pinkish 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  99 

red  color,  with  chocolate  red  or  pinkish  red  subsoils.  Both  strata 
are  calcareous.  They  are  first  bottom  soils  in  Texas  and  are  well 
adapted  to  cotton,  corn,  alfalfa,  forage  crops,  and  cabbage. 

Myatt  Series. — The  Myatt  soils  are  gray  to  dark  gray.  The 
subsoils  are  of  gray  to  mottled  gray  and  yellow  color  and  impervious 
character.  They  represent  the  poorest  drained  portion  of  the 
Coastal  Plain  stream  terraces.  They  lie  principally  above  overflow. 
When  drained  they  may  be  used  quite  profitably  for  sugar  cane, 
corn,  and  a  number  of  forage  crops. 

Ocklocknee  Series. — These  soils  are  dark  gray  to  brownish, 
with  brownish  or  mottled  brownish,  yellowish  and  gray  subsoils. 
They  occur  in  the  Coastal  Plains  and  are  subject  to  overflow.  Corn, 
oats,  and  forage  crops  are  grown. 

Osage  Series. — They  consist  of  dark  gray  to  almost  black 
alluvial  wash  from  the  sandstone  and  shale  soils  of  the  prairie 
regions.  They  produce  good  yields  of  general  farm  crops. 

Podunk  Series. — These  are  dark  brown  in  color  and  overlie 
lighter  brown  to  brownish  gray  or  yellowish  gray  subsoils.  They 
occur  as  rather  high  bottom  lands,  but  are  subject  to  overflow. 
They  produce  grass  and  heavy  truck  crops  well. 

Sarpy  Series. — These  soils  range  from  light  gray  to  nearly 
black.  They  possess  loose  silty  or  fine  sandy  subsoils  distinctly 
lighter  than  the  surface.  They  occur  in  the  bottoms  of  the  Missis- 
sippi and  Missouri  rivers  and  their  large  tributaries.  They  are  very 
productive  and  adapted  to  grains,  grasses,  and  alfalfa. 

Sharkey  Series. — These  soils  are  of  yellowish  brown  to  drab 
color,  with  mottled  rusty  brown,  bluish,  drab  and  yellowish  sub- 
soils, of  very  plastic  structure.  They  are  very  heavy  alluvial  soils  of 
the  Mississippi  river,  commonly  called  "  buckshot  land.''  They  are 
well  adapted  to  corn,  sugar  cane  and  cotton.  About  1,(500,000  acre.* 
have  been  mapped. 

Trinity  Series. — These  soils  are  dark  brown  to  black  first  bot- 
tom lands  mainly  derived  from  the  Huston  series.  The  organic 
matter  content  is  high  and  lime  is  usually  present.  They  occur 
as  flat  lands  in  shallow  valleys.  Large  crops  of  alfalfa,  cotton  and 
corn  are  produced  when  the  soil  is  well  drained.  The  area  mapped 
comprises  1,280,000  acres. 

Uvalde  Series. — These  soils  are  alluvial  and  occupy  broad  level 
flood  plains  in  Texas.  They  are  light  in  color  and  very  floury  to 
the  feel. 

Wabash  Series. — The  soils  are  of  a  dark  brown  to  black  color 


100  SOIL  PHYSICS  AND  MANAGEMENT 

and  high  in  organic  matter.  The  subsoils  are  lighter  drab  or  gray. 
They  occur  as  first  bottoms  along  the  Mississippi.  They  grow 
large  crops  of  grass  and  corn.  One  million  nine  hundred  acres  have 
been  mapped. 

Waverly  Series. — The  soils  are  light  gray  in  color  and  overlie 
gray  or  mottled  yellowish  and  grayish  subsoils.  They  occur  as  first 
bottom  land  along  streams  issuing  from  the  loessial  region  of  the  cen- 
tral prairie  states.  They  are  fairly  well  adapted  to  corn  and  grass. 

Wheeling  Series. —  These  soils  are  brown  to  yellowish  brown 
and  are  underlain  by  gravel  usually  within  3  feet  of  the  surface. 
They  occupy  the  gravel  terraces  along  the  streams  that  flowed  from 
the  ice-covered  regions. 

Yazoo  Series. — The  color  of  the  surface  soil  ranges  from  gray 
slightly  darkened  with  organic  matter  to  light  brown,  while  the 
subsoils  are  of  mottled  grayish,  rusty  brown  and  sometimes  bluish. 
They,  occur  in  the  flood  plains  of  the  Mississippi  river.  They  are 
well  suited  to  cabbage,  onions,  peas,  lettuce,  Irish  and  sweet  po- 
tatoes, cucumbers,  melons,  etc.  Cotton,  corn,  and  forage  crops  give 
good  results  on  the  heavy  types. 

VIII.    GREAT   PLAINS   REGION 

The  Great  Plains  Region  is  bounded  on  the  north  and  east  by 
the  Glacial  and  Loessial  province,  on  the  east  and  southeast  by  the 
Limestone  Valley  and  Uplands  province  and  the  Gulf  Coastal 
Plains,  and  on  the  west  by  the  Rocky  Mountains.  It  has  a  maximum 
width  of  600  miles.  In  altitude  it  varies  from  1000  to  6000  feet 
above  sea  level.  Where  not  eroded  it  is  a  level  or  gently  sloping 
plain.  There  are  areas  of  excessively  eroded  or  "  bad  land  "  to- 
pography. The  Great  Plains  region  extends  from  the  Rio  Grande  to 
Canada.  The  Upland  soils  are  divided  into  the  following  as  to 
origin : 

(1)  Residual  Material. — The  residual  soils  are  of  widespread 
occurrence  and  constitute  the  most  extensively  developed  and  im- 
portant province.  Owing  to  their  wide  distribution  these  soils  are 
subject  to  a  wide  variation  of  climatic  influences  that  have  been 
important  factors  in  their  formation.  The  series  are  as  follows : 

Bates  Series. — These  are  of  dark  gray  color,  while  the  subsoils 
are  yellowish  and  mottled  red  or  yellowish  or  buff  in  the  upper  part 
and  mottled  with  yellow  and  red  in  the  deeper  sections.  They  are 
treeless  and  of  undulating  topography.  The  crops  are  chiefly  corn, 
wheat,  flax,  and  oats. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  101 

Benton  Series. — The  soils  are  light  brown  or  grayish  brown  to 
gray  colored,  with  light  gray  subsoils.  They  are  derived  from  lime- 
stone and  shale  and  mostly  used  for  grazing. 

Boone  Series. — This  series  consists  of  light  gray  soils  of  low 
organic-matter  content  underlain  by  pale  yellowish  to  slightly  red- 
dish yellow  and  often  mottled,  porous  subsoils.  They  are  derived 
from  sandstone  and  shales.  The  soils  are  often  timbered  and  are 
frequently  thin  and  unproductive.  The  principal  crops  are  corn, 
oats,  wheat,  and  hay. 

Clark  Series. — This  series  includes  dark  gray  to  brown  or  black 
soils  and  grayish  calcareous  subsoils.  They  produce  fair  crops  of 
corn,  kafir,  wheat,  sorghum,  and  alfalfa. 

Crawford  Series. — These  comprise  residual  limestone  soils  of 
dark  brown  to  reddish  brown  surface  soils  and  reddish  brown  to 
red  subsoils.  Cotton,  corn,  wheat,  oats,  alfalfa,  clover,  and  timothy 
are  grown. 

Englewood  Series. — The  soils  are  of  brown  to  reddish  brown 
color.  The  subsoils  are  usually  reddish  brown  but  sometimes  brown. 
They  are  derived  from  shale  and  sandstone.  They  are  generally 
adapted  to  corn,  kafir,  sorghum,  and  hay. 

Epping  Series. — The  soils  are  white  or  light  gray  to  buff  and 
are  underlain  by  subsoils  of  similar  character.  They  are  derived 
from  shales  and  indurated  clays.  Wheat,  barley,  potatoes,  and 
alfalfa  are  the  principal  crops. 

Morton  Series. — The  soils  are  brown  in  color  and  contain  a 
high  content  of  organic  matter.  The  subsoils  are  light  brown- to 
gray  and  are  rich  in  lime.  They  are  derived  from  sandstone  and 
shales.  Wheat,  barley,  and  flax  are  the  principal  products.  More 
than  13,000,000  acres  have  been  mapped. 

Oswego  Series. — The  soils  arc  light  gray  to  dark  gray,  while 
the  subsoils  are  drab  to  yellow  and  are  compact  and  impervious. 
They  are  derived  from  shale  and  sandstone.  Wheat,  corn,  oats,  flax, 
rye,  and  potatoes  are  grown. 

Pierre  Series. — The  soils  of  this  series  are  light  brown  to  dark 
brown,  the  immediate  surface  often  being  light  gray.  They  are 
usually  compact  and  refractory.  The  subsoils  are  brown  and  com- 
pact and  grade  into  a  substratum,  of  partially  weathered  shale.  The 
surface  is  generally  irregular,  being  dissected  or  eroded  and  marked 
by  hills  and  ridges.  Drainage  is  generally  good.  The  typos  fre- 
quently contain  rather  excessive  amounts  of  alkali. 

Sidney  Series. — The  soils  consist  of  brown  surface  soils,  with 


102  SOIL  PHYSICS  AND  MANAGEMENT 

light  gray  to  white,  calcareous,  floury,  silty  clay  subsoils.  They  are 
derived  from  calcareous  conglomerate.  The  more  loamy  types  are 
good  for  general  farming. 

Summit  Series. — The  soils  are  dark  gray  to  black,  with  mot- 
tled yellow  and  gray  subsoils.  They  occupy  nearly  flat  to  sharply 
rolling  prairie?  and  are  derived  from  calcareous  shales.  Corn, 
wheat,  oats,  timothy,  clover,  and  alfalfa  are  the  principal  products. 

Vernon  Series. — The  soils  are  reddish  brown  to  red.  The 
subsoils  are  usually  red  but  sometimes  reddish  brown  or  brown  in 
the  upper  part.  Corn,  wheat,  oats,  cotton,  kafir  and  sorghum  are 
the  chief  products.  They  are  derived  from  sandstones  and  shales. 

(2)  Glacial  Material. — The  soils  derived  from  this  material 
do  not  occur  extensively  in  this  region.     They  are  represented 
by   a  single   series,   the  O'Neill.       The   soils  are  dark   gray  to 
brown,  underlain  by  light  brown  subsoils  resting  upon  sand  or 
gravel.     The  topography  varies  from  nearly  level  to  rough  and 
broken.    The  series  is  derived  from  glacial  drift  which  underlies  the 
loess.    The  deeper  members  have  a  high  value  for  small  grains,  corn, 
potatoes,  and  forage  crops. 

(3)  Lake-laid  Material. — The  soils  of  lacustrine  origin  are 
of  only  local  occurrence.     They  are  represented  by  three  series  of 
small  extent. 

(4)  Wind-laid  Material. — This  series  occupies  a  very  exten- 
sive area  in  Kansas,  Nebraska  and  South  Dakota.     The  principal 
series  are  the  Canyon,  Colby,  and  Valentine. 

Canyon  Series. — These  soils  are  light  brown  Or  ashy  brown 
and  the  subsoils  are  yellowish  gray.  They  are  mainly  derived  from 
loessial  material  and  are  adapted  to  grazing  and  locally  to  corn, 
milo,  kafir,  and  sorghum.  The  series  occurs  in  Kansas  and 
Nebraska. 

Colby  Series. — The  soils  are  ashy  gray  or  brownish  gray.  The 
upper  subsoil  is  similar  to  or  lighter  in  color.  They  are  derived 
from  loessial  deposits.  Wheat,  corn,  and  forage  crops  are  grown. 

Valentine  Series. — The  soils  consist  of  brown  to  dark  brown, 
with  light  brown  to  brown  and  usually  heavy  subsoils.  They  are 
adapted  to  corn,  potatoes,  truck,  and  hay  crops. 

(5)  Alluvial  Fan  and  Valley  Filling  Material. — These  have 
been  derived  from  the  great  areas  of  Tertiary  deposits  with  those 
less  extensive  areas  of  local  alluvial  fan  and  colluvial  material. 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  103 

They  are  unconsolidated,  but  include  certain  zones  of  material 
which  is  calcareous  and  more  or  less  indurated  or  cemented. 

Amarillo  Series. — These  include  chocolate  brown  to  reddish 
brown  soils,  with  brown  to  reddish  brown  subsoils.  The  subsoil 
grades  into  a  white  or  pinkish  white  calcareous  material  within 
three  feet  of  the  surface.  They  are  derived  from  sandstone,  shale, 
limestone,  and  crystalline  rock.  More  than  eleven  million  acres 
have  been  mapped. 

Colorado  Series. — The  soils  are  of  gray  to  reddish  brown  color 
and  contain  fine  quartz  and  feldspar  fragments.  The  subsoils  are 
reddish  brown.  They  grow  vegetables,  tree  fruits,  alfalfa,  and 
melons. 

Dawes  Series. — The  soils  are  ashy  gray  to  light  brown  in  color, 
with  white  to  pinkish  white  subsoils. 

Gannett  Series. — The  soils  are  light  brown,  with  yellowish 
sand  to  light  sandy  loam  subsoils.  They  are  mostly  utilized  for 
pasture. 

Greensburg  Series. — The  soils  are  brown  to  dark  brown  in 
color  and  the  subsoils  brown  to  yellowish  brown.  The  soils  are 
derived  mainly  from  Plains  Marl.  They  are  usually  treeless  and 
produce  wheat,  corn,  kafir,  and  sorghum. 

Pratt  Series. — The  soils  are  brown,  with  dark  reddish  brown 
rather  compact  sticky  subsoils,  usually  loam  to  clay  loam  in  tex- 
ture. They  retain  water  well  and  under  favorable  conditions  the 
soils  are  quite  productive,  giving  good  yields  of  kafir,  corn,  sorghum, 
and  wheat.  Nearly  2,000,000  acres  have  been  mapped. 

Richfield  Series. — The  soils  are  grayish  brown,  with  grayish 
brown  calcareous  subsoils.  They  are  retentive  of  moisture  and 
produce  wheat,  corn,  alfalfa,  and  forage  crops.  More  than  8,000,000 
acres  have  been  mapped. 

Rosebud  Series. — The  surface  soils  are  dark  gray  to  brown. 
The  subsoils  arc  light  colored,  almost  white,  and  very  calcareous. 
The  topography  ranges  from  undulating  to  steeply  rolling  and 
where  badly  eroded  constitutes  "  bad  land."  More  than  5,000,000 
acres  have  been  mapped. 

Zapata  Series. — The  soils  have  gray  calcareous  surface,  with 
subsoils  of  similar  color  and  texture.  They  have  a  very  low  value 
for  agricultiire.  They  aro  used  for  grazing. 

(6)  River  Flood  Plain  Material. — These  soils  are  the  flood 
plains  and  terraces  along  streams.  They  occur  widely  scattered 


104  SOIL  PHYSICS  AND  MANAGEMENT 

over  the  region,  but  are  especially  well  developed  as  the  wide 
valleys  along  the  larger  streams.  The  series  are  as  follows : 

Arkansas  Series. — This  series  includes  grayish  brown  or  dark 
brown  soils,  with  yellowish  brown  subsoils  resting  upon  gravels  and 
sands.  The  substratum  is  sometimes  so  near  the  surface  as  to 
cause  deficiency  of  moisture.  Soils  may  be  subject  to  overflow. 
Wheat,  corn,  forage  crops,  and  alfalfa  are  the  principal  crops. 

Cheyenne  Series. — The  soils  are  brown  with  lighter  brown  or 
yellow  subsoils  underlain  by  sands  and  gravels.  The  soils  occupy 
high  valley  terraces  laid  down  while  the  streams  were  choked  with 
ice.  They  are  productive  and  adapted  to  grazing,  small  grains, 
corn,  and  potatoes.  Under  irrigation  they  grow  alfalfa  and  fruits. 

Laurel  Series. — The  soils  are  dark  gray  to  brown  and  the  sub- 
soils are  usually  lighter  in  color  and  are  underlain  by  porous  gravel. 
Corn,  small  grains,  forage,  melons  and  cantaloupes  are  grown. 

Lincoln  Series. — The  soils  are  dark  brown  to  dark  gray  or 
nearly  black,  while  the  subsoils  are  dark  gray  to  brown.  Corn, 
forage  crops,  small  grains,  and  alfalfa  are  grown.  More  than 
2,300,000  acres  have  been  mapped. 

Tripp  Series. — The  soils  are  brown  to  light  gray,  while  the 
subsoils  are  light  gray  to  white.  They  are  of  alluvial  origin.  They 
are  adapted  to  corn,  wheat,  oats,  potatoes,  and  vegetables. 

Wade  Series. — The  soils  are  brown  to  dark  gray,  drab  or  dark 
brown,  while  the  subsoils  are  light  brown,  brown  or  gray  to  dark 
drab,  rather  heavy  and  compact.  The  crops  are  corn,  small  grain, 
flax,  potatoes,  and  alfalfa. 

IX.   ROCKY  MOUNTAIN  AND  PLATEAU  REGION 

This  region  covers  the  areas  of  elevated  mountains  and  plateaus 
extending  from  Canada  southward  to  the  lower  lying,  arid,  treeless 
plains  and  isolated  ranges  of  the  arid  region  of  Arizona  and  New 
Mexico. 

The  soils  vary  widely  in  character  owing  to  the  great  variety 
of  material  from  which  they  are  derived  and  the  number  of  agencies 
active  in  their  formation.  Weathering  in  places  has  given  rise  to  ex- 
tensive areas  of  residual  soils,  while  at  the  bases  of  the  mountains 
large  areas  of  colluvial  soils  are  found.  The  stream  valleys  have 
terraces  and  flood  plains,  while  the  broad  intermountain  basins 
have  extensive  deposits  of  sediments. 

(a)  Uplands. — San  Luis  Series. — The  soils  are  reddish 
brown  in  color  and  porous  in  structure  and  are  underlain  by  sands 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  105 

and  coarse  rounded  gravel.  They  are  derived  mainly  from  vol- 
canic rock. 

(b)  River  Flood  Plains. — Billings  Series. — The  soils  are  gray 
to  drab,  with  the  subsoils  similar  in  color,  structure  and  texture. 
They  are  derived  mainly  from  shales  and  sandstones,  and  are  adapted 
to  a  wide  range  of  crops  under  favorable  conditions  of  irrigation. 

Laramie  Series. — These  soils  are  light  brown  to  grayish  brown 
with  a  slight  reddish  cast.  The  subsoils  are  lighter  gray  or  more 
reddish,  sometimes  becoming  yellowish  gray,  and  are  underlain  by 
sand  or  sandy  loam  with  gravel.  They  are  treeless  plains. 

Mesa  Series. — The  soils  are  pinkish  red  or  reddish  gray  to 
light  reddish  brown.  The  subsoils  are  of  lighter  reddish  gray  or 
gray  color  and  heavier  texture.  Where  irrigated,  fruits,  alfalfa, 
and  general  farm  crops  do  well. 

X.   NORTHWESTERN   INTERMOUNTAIN   REGION 

This  region  lies  between  the  Pacific  Coast  region  on  the  west, 
the  Kocky  Mountain  region  on  the  north  and  east,  and  the  Great 
Basin  region  on  the  south. 

The  rocks  of  this  region  are  mostly  effusive  or  volcanic  and  the 
soil  material  is  derived  largely  from  these,  either  by  weathering  of 
solid  material  or  from  fragments  ejected  from  volcanoes. 

(a)  Uplands. — Ephrata  Series. — These  soils  are  of  light  gray- 
ish brown  to  yellowish  brown  color,  while  the  subsoils  are  porous  but 
compact.     They  consist  largely  of  glacial  subangular  or  rounded 
gravel  or  boulders. 

Quincy  Series. — The  soils  are  grayish  brown  and  usually  of 
loose  porous  structure.  The  subsoils  are  similar  in  color  and  tex- 
ture but  slightly  more  compact.  They  are  wind-laid  material. 

Walla  Walla  Series. — This  series  consists  of  sticky,  brown  to 
dark  brown  soils  about  three  feet  deep  underlain  by  yellow  silt  loam 
subsoils  which  are  often  sticky  and  plastic.  The  topography  is  high 
rolling  hills.  The  soil  material  is  wind-laid.  Wheat,  barley,  and 
oats  are  the  principal  crops. 

Winchester  Series. — The  soils  and  subsoils  of  this  series  are 
dark  gray  to  nearly  black  and  consist  mainly  of  dark-colored  angular 
fragments  of  basalt.  The  fine  material  is  wind-laid. 

(b)  River  Flood  Plains. — Boise  Series. — Soils  are  of  light 
gray  to  light  brown  color.     The  subsoils  are  similar  to  the  soils  in 
color.    They  are  underlain  by  a  calcareous  hardpan  stratum.    They 
are  of  alluvial  origin. 


106  SOIL  PHYSICS  AND  MANAGEMENT 

Caldwell  Series. — The  soils  range  in  color  from  gray  to  dark 
gray  or  black.  The  subsoils  are  usually  of  somewhat  lighter  shade, 
varying  from  light  gray  to  drab,  and  are  underlain  by  gravel. 
Small  grains,  timothy  and  other  grasses,  alfalfa,  potatoes,  and 
sugar  beets  are  grown. 

Yakima  Series. — The  soils  range  from  light  to  grayish  brown 
to  yellowish  brown  or  light  brown  in  color.  They  are  usually  tree- 
less plains  and  of  alluvial  origin.  The  immediate  surface  material 
is  derived  from,  basaltic  or  other  eruptive  rocks. 

XI.  GREAT  BASIN  REGION 

This  region  embraces  practically  all  of  the  Great  Basin  of  In- 
terior Drainage.  It  includes  all  of  Nevada  with  the  exception  of 
the  extreme  southeastern  parts,  the  western  part  of  Utah,  a  small 
part  of  southwestern  Idaho,  the  south  central  part  of  Oregon,  and 
the  greater  part  of  the  eastern  margin  of  California. 

The  region  is  characterized  by  numerous  isolated  ridges  and 
mountain  ranges  running  in  a  general  north  and  south  direction, 
arid  treeless  plains  and  intermittent  streams  which  disappear  in  the 
gravelly  or  sandy  soil  or  discharge  into  broad  lake  basins  mostly 
without  outlets.  Many  of  these  basins  were  lakes  in  Quaternary  time. 

The  soils  are  classified  according  to  the  agencies  contributing 
to  their  formation. 

(a)  Uplands. — Bingham    Series. — This    series    occupies    the 
lower  mountain  and  upper  valley  slopes  and  valley  terraces  or  plains 
and  is  formed  from  mountain  wash  and  delta  cone  deposits.    They 
are  quite  fertile  when  irrigated  and  are  adapted  to  alfalfa,  .grains, 
sugar  beets,  vegetables,  and  fruits. 

(b)  River    Flood    Plains. — Jordan    Series. — The    soils    are 
usually  dark  in  color  but  sometimes  light  gray  or  reddish,  the 
heavier  lower  lying  members  being  underlain  by  gray,  black,  yellow 
or  red  compact  heavy  and  often  calcareous  subsoils.    They  are  de- 
voted to  grains,  alfalfa,  fruits,  and  truck  crops. 

XII.    ARID  SOUTHWEST   REGION 

This  region  covers  the  southwestern  third  of  Arizona,  a  large 
area  in  south  central  New  Mexico  and  in  northwestern  Texas.  It 
includes  also  a  small  area  in  southeastern  Nevada  and  the  south- 
eastern extremity  of  California. 

The  region  consists  of  sandy,  gravelly  sloping  or  flat  treeless 
plains  from  which  rise  frequent  low  rounded  hills  and  occasional 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  107 

flat  topped  mesas  and  many  isolated,  elongated  mountain  ridges. 

(a)  Uplands. — Glendale  Series. — These  soils  range  from  light 
gray  or  grayish  brown  to  dark  brown  or  chocolate  in  color  and  are 
underlain  by  gray  to  light  brown  highly  calcareous  subsoils.    When 
irrigated  they  produce  alfalfa,  forage  crops,  vegetables,  grapes  and 
citrous  fruits. 

Imperial  Series. — The  soils  are  generally  of  light  or  reddish 
color,  the  heavier  members  being  compact  and  plastic,  poorly 
drained  and  alkaline.  The  soil  material  represents  old  lake  deposits 
derived  mainly  from  sandstone  and  shales. 

Indio  Series. — The  soils  are  light  gray  to  slate  colored,  porous, 
and  underlain  by  coarser  sand.  They  are  derived  from  granites 
mixed  with  shales  and  sandstones.  Melons,  sweet  potatoes,  truck 
crops,  etc.,  are  grown  under  irrigation. 

Yuma  Series. — These  soils  are  usually  rather  compact.  The 
subsoil  is  similar  to  the  soil  except  that  at  a  depth  of  2  to  6  feet 
layers  occur  that  have  the  particles  slightly  cemented  together  with 
calcium  carbonate.  They  generally  occupy  mesh  lands.  They  are 
adapted  to  citrous  fruits,  figs,  grapes,  and  vegetables. 

(b)  River    Flood    Plains. — Gila    Series.— The    soils    of    the 
lighter  types  are  prevailingly  of  light  yellowish  brown,  light  grayish 
brown  or  slightly  reddish  brown  color  and  porous  structure.     The 
heavier  types  range  in  color  from  brown  or  chocolate  brown  to  dark 
gray  or  black  and  are  compact.     The  series  occupies  stream  flood 
plains  and  second  bottoms  or  recent  terraces. 

XIII.    PACIFIC   COAST   REGION" 

This  region  includes  the  area  of  California,  Oregon  and  Wash- 
ington west  of  the  Cascade,  Sierra  Nevada,  Sierra  Madre  and  San 
Jacinto  Mountains.  A  broad  valley  extends  almost  the  entire 
length  with  only  slight  interruptions. 

(a)  Upland. — Altamont  Series. — Soils  are  light  brown  to  dark 
brown  in  color  with  a  reddish  tinge  when  wet.  Subsoil  is  heavy, 
rather  compact  reddish  brown  or  light  brown  clay  loam  or  clay. 
The  series  occupies  hilly  to  mountainous  regions.  The  members 
of  this  series  are  residual,  being  derived  from  sandstone  and  shales. 
Hay  and  fruits  are  grown. 

Corning  Series. —  The  soils  are  of  reddish  brown  or  red  to  deep 
red  color,  rather  shallow,  easily  puddled,  and  hard  to  handle  except 
under  proper  moisture  conditions.  The  subsoils  are  reddish  brown 
to  deep  red.  of  heavy  and  compact  structure  and  impervious  to 
moisture.  The  soils  occupy  sloping  to  undulating  and  hilly  and 


108  SOIL  PHYSICS  AND  MANAGEMENT 

dissected   upland   terraces   and   valley   plains.      They   arej  poorly 
adapted  to  general  fanning. 

Everett  Series. — These  soils  range  from  light  brown  to  light 
reddish  brown  in  color  and  are  of  silky  texture  and  porous  structure. 
Large  amounts  of  organic  matter  often  occur  in  the  immediate  sur- 
face. The  subsoils  are  light  brown  to  gray  and  usually  gravelly  and 
porous.  The  material  is  of  glacial  origin  and  is  derived  from 
basaltic  and  intrusive  rocks.  Heavy  forests  abound.  Some  of  the 
less  porous  types  are  adapted  to  dairying,  orchard,  and  small  fruits. 

Fresno  Series. — The  soils  vary  in  color  from  gray  to  light  ash 
brown,  the  heavier  low-lying  members  sometimes  assuming  a  dark 
gray  color  as  a  result  of  accumulations  of  organic  matter.  They 
are  usually  free  from  gravel ;  a  layer  of  white  or  bluish  gray,  im- 
pervious, calcareous,  alkali-carbonate  hardpan  varying  in  thickness 
from  a  fraction  of  an  inch  to  several  inches  separates  the  soil  and 
subsoil.  The  hardpan  slowly  softens  under  irrigation,  but  is  nor- 
mally impenetrable  to  the  roots  of  growing  plants.  They  occur  as 
old  alluvial  or  colluvial  deposits  derived  from  granite  rocks.  If 
the  hardpan  is  not  too  near  the  surface  and  irrigation  is  practiced 
alfalfa,  grapes,  fruits,  and  vegetables  do  well. 

Hanford  Series. — The  soils  are  generally  of  light  grayish 
brown  or  buff  to  light  brown  color,  the  heavier  members  carrying 
considerable  organic  matter  and  becoming  dark  gray  to  nearly  black 
when  wet.  They  are  micaceous,  smooth  to  the  touch,  friable,  and 
of  porous  structure,  generally  free  from  gravel  or  boulders.  The 
soil  material  represents  recent  alluvial  stream  deposits  derived 
mainly  from  granite  rocks.  When  irrigated  they  are  well  adapted  to 
tree  fruits,  raisin  and  table  grapes,  nuts,  vegetables  and  truck  crops. 

Hesson  Series. — The  soils  are  dark  reddish  brown  and  under- 
lain by  yellowish  brown  to  reddish  brown  subsoils  of  compact  struc- 
ture. Rounded  gravel  and  small  boulders  are  common  on  the  sur- 
face. The  series  occupies  eroded  terraces  of  undulating  to  rolling 
topography,  usually  several  hundred  feet  above  the  valley  bottoms. 
The  material  has  been  derived  mainly  from  basaltic  rocks  and  con- 
sists of  old  alluvial  or  marine  terrace  deposits.  They  are  well 
adapted  to  general  farming  and  orchard  fruits. 

Melbourne  Series. — These  soils  are  light  brown  to  reddish 
b'rown  in  color  and  often  dark  brown  in  the  immediate  surface. 
When  wet  they  are  sticky  and  untractable,  but  under  favorable 
moisture  conditions  are  easily  tilled.  They  are  derived  princi- 
pally from  shales  and  sandstones.  The  topography  varies  from 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  109 

rolling  to  hilly.    Much  is  too  rough  for  the  use  of  farm  machinery. 

Maracopa  Series. — The  soils  range  from  dark  gray  through 
the  darker  shades  of  brown  and  chocolate  to  black.  They  are  loose, 
porous,  ordinarily  well  drained  and  free  from  alkali.  The  soils 
represent  assorted,  colluvial  material,  largely  derived  from  granite 
rocks.  When  water  is  sifpplied  they  are  well  adapted  to  fruits, 
vines  and  general  farm  crops. 

Lynden  Series. — The  soils  are  light  brown  to  reddish  brown 
and  in  the  lighter  textured  sandy  types  often  light  gray  on  the 
.surface.  The  subsoil  is  sandy  or  gravelly.  Drainage  is  usually  ex- 
cessive. The  soils  are  derived  principally  from  stratified  deposits 
of  sand  and  gravel  formed  by  glacial  outwash.  They  occupy  gently 
rolling  upland  terraces  and  plains  formerly  glacial  flood  plains, 
now  dissected  and  eroded.  All  types  are  suited  to  agriculture. 

Olympic  Series. — These  soils  are  light  brown  and  brown  with 
a  reddish  cast.  The  subsoils  are  generally  of  compact  structure  and 
somewhat  lighter  in  color  than  the  soils.  They  are  derived  mainly 
from  basaltic  rock.  The  topography  is  rough  to  mountainous. 
Rainfall  is  abundant  and  the  soils  are  heavily  forested.  When  not 
too  rough  they  may  be  used  for  general  farming  and  dairying. 

Oxnard  Series. — The  soils  are  generally  of  dark  color  and 
compact  structure,  and  though  sometimes  underlain  by  porous 
subsoils  of  light  texture,  are  generally  underlain  by  heavier  sub- 
soils. The  subsoils  lack  the  red  color  and  adobe  structure  of  the  sub- 
soils of  the  Placentia  series.  They  represent  alluvial  delta  plain 
deposits.  These  are  particularly  adapted  to  the  production  of  lima 
beans.  Sugar  beets,  barley,  and  vegetables  do  well. 

Placentia  Series. — The  soils  are  reddish  brown  or  brown  and 
underlain  by  heavy,  compact,  red  loams  or  clay  loams  of  tough, 
impervious  adobe  structure.  The  soil  material  consists  of  alluvial 
outwash,  deposits  of  intermittent  or  torrential  mountain  streams. 
They  are  derived  from  granitic  rocks.  They  are  tilled  with  diffi- 
culty but  retain  moisture  well  and  produce  grains,  citrous  fruits, 
and  beans. 

San  Joaquin  Series. — The  soils  are  prevailingly  red  and  fre- 
quently gravelly.  Both  (he  finer  soil  particles  and  gravel  are 
rounded.  The  soils  are  underlain  at  depths  ranging  from  2  to 
3  feet  by  red  or  mottled  indurated  clay  or  sandy  layers  and  some- 
times by  gravel  and  cobbles  cemented  by  iron  salts  into  a  dense, 
impenetrable  hardpan.  Some  of  the  members  are  used  in  the 


110  SOIL  PHYSICS  AND  MANAGEMENT 

production  of  citrous  and  stone  fruits,  figs,  grapes,  small  fruits, 
and  truck  crops. 

Stockton  Series. — The  lighter  members  of  this  series  have  a 
buff  to  reddish  or  chocolate  brown  color.  The  heavier  members 
generally  exhibit  a  marked  adobe  structure,  are  usually  free  from 
gravel,  and  range  from  dark  brown  to  dark  gray  or  black  in  color. 
The  heavier  members  are  devoted  mainly  to  the  production  of 
grains  and  hay. 

Redding  Series. — The  soils  range  from  reddish  gray  to  deep 
red,  are  usually  gravelly  and  sometimes  carry  large  amounts  of 
alkali  and  partially  indurated  clay-iron  hardpan.  Strawberries 
and  bramble  fruits  yield  abundantly. 

Whatcom  Series. — The  soils  of  the  Whatcom  series  are  of  a 
deep  reddish  brown  color  and  prevailingly  of  fine  texture  and  rather 
compact  structure.  The  surface  soil  is  often  dark  brown  or  nearly 
black.  Subsoils  consist  of  drab  to  gray  plastic  and  compact  heavy 
silts,  the  upper  portion  carrying  some  gravel  and  glacial  boulders. 
Soils  are  derived  from  compact  glacial  drift  and  occupy  areas  of 
undulating  to  rolling  upland.  The  soils  are  adapted  to  small  and 
orchard  fruits,  potatoes,  vegetables  and  hay  crops. 

Willows  Series. — The  soils  range  in  color  from  brown  to  red- 
dish brown  or  dark  chocolate  brown  and  are  free  from  gravel. 
The  subsoils  are  light  brown  to  reddish  brown  or  sometimes  yel- 
lowish and  mottled  with  gray.  They  have  a  compact,  relatively 
impervious  structure  and  often  contain  lime  and  gypsum-.  They 
are  derived  mainly  from  calcareous  shales,  sandstone,  and  shaly 
sandstone  rocks.  Where  well  drained  and  free  from  alkali,  they  are 
well  adapted  to  the  production  of  alfalfa,  grains  and,  with  the  ex- 
ception of  those  areas  of  extremely  heavy  texture,  sugar  beets. 

Yolo  Series. — This  series  embraces  alluvial  soils  of  brown  or 
dark  brown  color,  underlain  by  lighter  brown  subsoils.  The  types 
have  been  derived  from  schists  and  other  metamorphic  rocks,  with 
some  material  from  shaly  sandstones  and  shales.  Where  capable 
of  irrigation,  fruits,  vegetables,  and  forage  crops  can  be  grown. 

(b)  River  Flood  Plains — Chehalis  Series. — The  soils  are  of 
recent  alluvial  origin,  occupying  stream  valleys,  traversing  the 
region  of  residual  basaltic  soils  that  vary  from  gray  or  drab  to 
reddish  brown,  some  of  the  heavier  types  containing  very  much 
organic  matter  and  showing  a  dark  brown  to  black  color.  The  sub- 
soils vary  from  yellow,  gray  or  mottled  to  light  brown,  dark  brown, 


CLASSIFICATION  BY  THE  BUREAU  OF  SOILS  111 

or  reddish  brown  to  black  in  color.    These  soils  are  very  productive. 

Puget  Series. — The  soils  are  brown  to  grayish  brown  or  drab 
and  frequently  mottled  with  iron  stains.  The  heavier  members  are 
of  rather  compact  and  tenacious  structure,  containing  a  large 
amount  of  organic  matter,  and  are  usually  friable  under  cultiva- 
tion. The  subsoils  are  light  brown  to  drab  or  gray  marked  with 
iron  stains.  They  occupy  flood  plains  in,  the  vicinity  of  estuaries 
or  stream  outlets.  They  are  very  productive  and  are  classed  among 
the  very  best  soils  of  the  region.  Oats,  forage,  hay  and  truck  crops 
and  fruits  all  do  well. 

Sacramento  Series. — The  soils  are  dark  gray,  drab  or  black, 
often  contain  large  quantities  of  organic  matter  and  are  six  feet 
or  more  in  depth.  The  series  occupies  stream  bottoms  and  river 
flood  plains.  Alkali  salts  are  sometimes  encountered.  Where  pro- 
tected by  levees,  the  soils  are  productive  and  adapted  to  the  inten- 
sive production  of  sugar  beets,  truck  crops,  beans,  hops,  potatoes 
alfalfa,  and  prunes,  pears  and  other  fruits. 

Salem  Series. — The  soils  are  dark  brown  to  black  in  color  and 
underlain  by  compact  reddish  yellow  subsoils  or  by  sands  and 
gravels.  They  are  recent  alluvial  deposits  derived  from  basaltic 
rocks,  drains,  truck  crops  and  hops  are  the  principal  crops. 

QUESTIONS 

1.  What  is  a  soil  Region?    A  Province? 
•2.  How  many  of  each  ? 

3.  Define  a  soil  series. 

4.  Define  a  soil  class. 

5.  What  is  a  soil  type? 

0.  Where  does  the  Cecil  series  occur? 

7.  What  are  its  characteristics? 

8.  What  are  the  characteristics  of  the  Do  Kalb  series? 

9.  Give  characteristics  of  Clarksville  series. 

10.  Give  characteristics  of  Carrington  series. 

11.  Give  characteristics  of  De  Kalb  scries. 

12.  Give  characteristics  of  Marshall  series. 
1.3.  (Jive  characteristics  of  Miami  scries. 

14.  Give  characteristics  of  Volusia  series. 

15.  Give  characteristics  of  Williams  series. 
Ifi.  Give  characteristics  of  Norfolk  series. 

17'.  Give  characteristics  of  Orangeburg  series. 

18.  Where  is  the  Great  Plains  region?     Give  two  series. 

10.  Where  is  the  Arid  Southwest  region? 

20.  Locate  the  Piedmont  Plateau  Province. 

21.  Locate  the   Appalachian   Mountain   and    Plateau   Province.      What   are 

the  two  principal  series? 

REFERENCE 

Marbut.  C.  F.,  Bennett.  H.  TT.,  Lapham,  .T.  E..  and  Lapham.  M.  TI..  Bulletin 
9fi,  Bureau  of  Soils  IT.  S.  D.  A. 


CHAPTER  IX 

SUB-PROVINCES,  CLASSES,  TYPES  AND  SURVEYS 

IN  working  out  the  classification  of  soils  in  detail  in  a  single 
state,  it  may  be  necessary  to  make  other  divisions,  or  sub-provinces, 
the  soils  of  which  have  a  common  origin,  but  differ  from  those  of 
other  sub-provinces  in  some  fundamental  characteristics. 

Sub-provinces. — On  this  basis  the  glacial  and  loessial  province 
of  Illinois  has  been  divided  into  the  following  sub-provinces: 
(1)  Unglaciated,  comprising  three  areas,  the  largest  being  in  the 
south  end  of  the  state;  (2)  Illinoisan  Moraines,  including  the 
moraines  of  the  Illinoisan  Glaciation;  (3)  Lower  Illinoisan  Glacia- 
tion,  covering  the  south  third  of  the  state;  (4)  Middle  Illinoisan; 
(5)  Upper  Illinoisan;  (6)  Pre-Iowan,  but  now  believed  to  be  part 
of  the  Upper  Illinoisan;  (7)  lowan  Glaciation;  (8)  Deep  Loess 
Area,  including  a  zone  a  few  miles  wide  along  the  Wabash,  Illinois 
and  Mississippi  rivers;  (9)  Early  Wisconsin  Moraines;  (10)  Late 
Wisconsin  Moraines;  (11)  Early  Wisconsin  Glaciation;  (12)  Late 
Wisconsin  Glaciation;  (13)  Old  River  Bottom  and  Swamp  Lands, 
found  in  the  older  or  Illinois  Glaciation;  (14)  Sand,  Late  Swamp 
and  Bottom  Lands,  those  of  the  Wisconsin  and  lowan  Glaciation ; 
(15)  Gravel  Terraces  formed  by  overloaded  streams  draining  from 
the  glaciers  and  gravel  outwash  plains;  (16)  Lacustrine  Deposits, 
formed  by  Lake  Chicago  or  the  enlarged  Lake  Michigan. 

Soil  Classes. — The  soils  of  these  sub-provinces  are  divided 
into  classes  based  primarily  on  texture.  The  classes  are  as  follows: 

(1)  Peats,   (2)   Peaty  Loams,   (3)   Mucks,   (4)   Clays,   (5)   Clay 
loams,   (6)   Silt  loams,    (7)   Loams,   (8)    Fine  sandy  loams,   (9) 
Sandy  loams,  (10)  Sands,  (11)  Gravelly  loams,  (12)  Gravels,  (13) 
Stony  loams.    These  are  further  divided  into  soil  types. 

Soil  Types. — A  soil  type  is  the  unit  of  soil  classification.  It 
is  a  soil  unit  which  throughout  the  area  has  the  same  physical, 
chemical  and  biological  characteristics.  In  the  establishment  of 
soil  types,  the  following  factors  are  taken  into  account:  (1)  Origin, 
whether  residual,  cumulose,  colluvial,  sedimental,  glacial  or  eolial. 

(2)  The  topography  or  lay  of  the  land.     (3)  The  native  vegetation, 
as  forest  or  prairie.     (4)  The  strata  or  character  of  surface,  sub- 
surface or  subsoil.      (5)    Physical  composition  or  texture  of  the 

112 


SUB-PROVINCES,  CLASSES,  TYPES  AND  SURVEYS        113 

different  strata.  (6)  The  structure  or  granulation.  (7)  The 
color  of  the  strata.  (8)  The  natural  drainage.  (9)  The  amount 
of  organic  matter  present.  (10)  The  agricultural  value,  based 
upon  its  natural  productiveness.  (11)  The  ultimate  chemical  com- 
position and  reaction,  whether  acid,  neutral  or  alkaline. 

Naming  of  Soil  Types. — At  first  thought  it  might  seem  a  very 
easy  and  simple  matter  to  name  soil  types.  It  is  on  a  single  farm, 
but  the  difficulty  increases  with  the  size  of  the  area,  the  number  of 
different  soils,  and  the  detail  desired.  From  the  standpoint  of 
everyone  concerned,  but  more  especially  from  that  of  the  farmer, 
the  simpler  and  more  expressive  the  name  the  better,  and  the  easier 
it  will  be  to  associate  it  with  the  soil.  To  a  certain  extent  the  name 
should  be  descriptive  of  the  type.  According  to  the  nomenclature  in 
use  by  the  Bureau  of  Soils,  names  of  soil  types  usually  consist  of 
two  parts,  the  series  name  and  the  class  name,  with  sometimes  a 
modifying  word  included.  The  series  name  is  that  of  some  locality 
where  the  soil  in  question  was  first  found  or  where  it  is  well  de- 
veloped. This  gives  names  as  follows:  Cecil  silt  loam,  Marshall 
fine  sand,  Marshall  black  clay  loam,  etc. 

The  above  system  of  naming  is  applicable  to  extensive  areas, 
but  for  a  limited  area,  such  as  a  single  state,  a  more  expressive 
system  may  be  devised.  After  the  texture,  one  of  the  most  striking 
characteristics  of  soils  is  the  color.  In  the  naming  of  soils  in 
Illinois,  a  combination  of  color  and  texture  together  with  other 
descriptive  terms,  when  necessary,  has  been  adopted  as  convoying 
the  most  meaning  to  those  who  use  the  name.  Without  ever  having 
seen  it,  the  name,  so  constructed,  gives  a  very  good  idea  of  the 
character  of  the  soil.  As  illustrations,  gray  silt,  loam  on  tight  clay, 
yellow  silt  loam,  brown  silt  loam  on  gravel,  and  medium  peat  on 
rock  may  be  given. 

There  are  such  great  variations  in  color  that  these  color  dis- 
tinctions do  not  always  strictly  apply.  The  soil  on  rolling  and  hilly 
land  is  usually  of  a  yellow  color  either  on  the  surface  or  immediately 
beneath  the  surface-  soil,  so  that  those  aro  called  yellow  silt  loams, 
yellow  fine  sandy  loams,  etc.  The  undulating  timber  soils  are  yellow 
or  grayish  and  the  term  or  name  yellow-gray  is  applied  to  them. 
Prairies  are  either  dark  gray,  brown,  or  black.  The  use  of  the 
term  "on"  as  part  of  a  soil  typo  name  indicates  the  presence  of  cer- 
tain substrata  within  30  inches  of  the  surface.  If  the  term  "  over  " 
is  used,  the  material,  such  as  sand,  gravel,  or  rock,  is  more  than  30 
inches  below  the  surface. 
8 


114  SOIL  PHYSICS  AND  MANAGEMENT 

• 

Classes,  Types  and  Phases  in  Illinois. — It  may  be  of  interest 
to  give  the  classes  of  soils  and  their  limits,  with  some  of  the  types 
and  their  phases  as  used  in  the  Illinois  classification.  In  numbering 
soil  types  a  system  somewhat  similar  to  the  Dewey  library  system 
has  been  used,  in  which  the  whole  numbers  represent  the  sub- 
provinces  and  types,  and  the  decimals,  the  phases.  To  illustrate: 
A  soil  has  the  number  726.5.  The  number  7  means  that  it  occurs 
in  the  lowan  glaciation,  the  26  that  it  is  brown  silt  loam,  and  .5 
that  rock  is  found  less  than  30  inches  below  the  surface.  These 
numbers  are  convenient  for  use  upon  the  soil  maps  in  numbering 
small  soil  areas. 

Peats — consisting  of  35  per  cent  or  more  of  organic  matter  sometimes 
mixed  with  some  sand,  silt  or  clay. 

1.  Deep  peat — with   peat  more  than   30   inches   in   depth.     It   is   best 

drained  by  open  ditches  because  of  the  unequal  settling  of  tile, 
thus  getting  them  out  of  line. 

2.  Medium  peat  on  clay — with  peat  between  12  and  30  inches  in  depth. 

Tile   drains   are   usually   below  the  peat  and   therefore   have  a 
good  bed. 

2.1  Medium  peat  on  clayey  sand. 

2.2  Medium  peat  on  sand. 

2.4  Medium  peat  on  gravel. 

2.5  Medium  peat  on  rock. 

2.6  Medium  peat  on  marl. 

3.  Shallow  peat  on  clay — with  peat  6  to  12  inches  deep.     It  may  be 

plowed   sufliciently  deep  to   bring  up   some   clay   for   supplying 
potassium. 

3.1  Shallow  peat  on  clayey  sand. 

3.2  Shallow  peat  on  sand. 

3.4  Shallow  peat  on  gravel. 

3.5  Shallow  peat  on  rock. 

3.6  Shallow  peat  on  marl. 

Peaty  loams — consisting  of  15  to  35  per  cent  of  organic  matter  with 
a  large  proportion  of  sand  and  very  little  silt  or  clay. 
10.  Peaty  loam  on  clay. 

10.1  Peaty  loam  on  clayey  sand. 

10.2  Peaty  loam  on  sand. 

10.4  Peaty  loam  on  gravel. 

10.5  Peaty  loam  on  rock. 

Mucks — 15  to  35  per  cent  of  decomposed  organic  matter  mixed  with 
much  clay  and  silt. 
13.  Muck  on  clay. 

13.1  Muck  on  clayey  sand. 

13.2  Muck  on  sand. 
13.5     Muck  on  rock. 

Clays — soils  with  more  than  25  per  cent  of  clay,  usually  containing 
much  sift. 

15.  Drab  clay. 

15.1  Sandy  drab  clay. 

15.2  Gravelly  drab  clay. 

15.3  Drab  clay  on  sand. 
Ifi.  <C,ray  clay. 


SUB-PROVINCES,  CLASSES,  TYPES  AND  SURVEYS         115 

Clay  loams — soils  with   from    15  to  25  per  cent  of  clay   with  much 
silt  and  some  sand. 

20.  Black  clay  loam. 

20.1  Sandy  black  clay  loam. 

20.2  Gravelly  black  clay  loam. 

21.  Drab  clay  loam. 

21.2     Drab  clay  loam  on  sand. 

22.  dray  clay  loam. 

23.  Red  broirn  clay  loa-m. 

24.  Yellow  gray  clay  loam. 

Silt  loams — soils  with  more  than  50  per  cent  of  silt  and  less  than  15 
per  cent  of  clay,  mixed  with  some  sand. 

25.  Black  silt  loam. 

25.1     Black  silt  loam  on  clay. 
20.  Broim  silt  ham. 

2(i.l     Brown  silt  loam  on  clay. 
2(i.2     Brown  silt  loam  on  sand. 
2(i.4     Brown  silt  loam  on  gravel. 
20.5     Brown  silt  loam  on  rock. 

27.  Broir-n  silt  loam  over  gravel. 

28.  Broir-n-gray  silt  loam  on  tight  clay. 
20.  Drab  silt  Imim. 

,        2!).l     Drab  silt  loam  on  clay. 

30.  (Iray  silt  loam  on  tight  clay. 

31.  Deep  gray  silt  loam. 

32.  Light  gray  silt  loam  on  tight  clay. 

32.1      White  silt  loam  on  tight  clay. 

33.  (!  ray-red  silt  loam  on  tight  elay. 

34.  Yclloir-gray  silt  loam. 

34.1  Yellow  gray  silt  loam  on  clay. 

34.2  Yellow  gray  silt   loam  on  sand. 

34.4  Yellow  gray  silt  loam  on  gravel. 

34.5  Yellow  gray  silt  loam  on  rock. 

35.  Yclloir  silt  loam. 

35.1  Yellow  silt  loam  on  clay. 

35.2  Yellow  silt  loam  on  sand. 

35.4  Yellow  silt  loam  on  gravel. 

35.5  Yellow  silt  loam  on  rock. 
3(5.   Yelloir-f/ray  silt  loam  over  grarel. 
37.    Yelloir-broirn  silt  loam. 

44.  Yelloio-gray  fine  sandy  silt  loam. 

45.  Yclloir  fine  sandy  silt  loam. 

Loams — soils  with  from  30  to  50  per  cent  of  sand  and  with  less  than 
15  per  cent  of  clay.  No  one  constituent  predominates  sutliciently  to  impart 
very  definite  characteristics. 

50.  Black  mi.red  loam. 

50.1  Black  mixed  loam  on  clay. 

50.2  Black   mixed  loam  on  sand. 
50.5     I'.lack  mixed  loam  on   rock. 

51.  Broirn  loam. 

51.1  Brown  loam  on  clay. 

51.2  Brown  loam  on  silt. 

51.3  Brown  loam  on  sand. 

51.4  Brown  loam  on  gravel. 

51.5  Brown  loam  on  rock. 


116  SOIL  PHYSICS  AND  MANAGEMENT 

52.  Gray  loam. 

53.  Yellow  loam. 

54.  Mixed  loam — usually  first  bottom  land. 

Sandy  loams — soils  with  50  to  75  per  cent  of  sand  and  less  than  15 
per  cent  of  clay. 

60.  Brown  sandy  loam. 

60.1  Brown  sandy  loam  on  clay. 

60.2  Brown  sandy  loam  on  sand. 

60.4  Brown  sandy  loam  on  gravel. 

60.5  Brown  sandy  loam  on  rock. 

60.6  Light  brown  sandy  loam. 

61.  Black  sandy  loam, 

62.  G*ay  sandy  loam. 

64.  Yellow-gray  sandy  loam. 

64.4  Yellow-gray  sandy  loam  on  gravel. 

64.5  Yellow-gray  sandy  loam  on  rock. 

65.  Yellow  sandy  loam. 

65.5     Yellow  sandy  loam  on  rock. 

66.  Brown  sandy  loam  over  gravel. 

67.  Yellow-gray  sandy  loam  over  gravel. 

68.  Brown-gray  sandy  loam  on  tight  clay. 

Fine  sandy  loams — soils  with  from  50  to  75  per  cent  of  fine  sand  and 
with  much  silt  and  less  than  15  per  cent  of  clay. 

70.  Black  fine  sandy  loam. 

71.  Brown  fine  sandy  loam. 

71.5     Brown  fine  sandy  loam  on  rock. 

72.  Gray  fine  sandy  loam. 

73.  Mixed  fine  sandy  loam. 

74.  Yellow-gray  fine  sandy  loam. 

75.  Yellow  fine  sandy  loam. 

76.  Mixed  sand  and  loess. 

77.  Brown  fine  sandy  loam  over  sand. 

Sands — soils  with  more  than  75  per  cent  of  sand. 

80.  River  sand. 

81.  Dune  sand. 

82.  Beach  sand  (Lake  Michigan). 

83.  Residual  sand. 
86.  Fine  dune  sand. 

Gravelly  loams — soils  with  25  to  50  per  cent  of  gravel  with  much 
sand  and  little  silt. 

90.  Gravelly  loam. 

Gravels — soils  with  more  than  50  per  cent  of  gravel  and  much  sand. 

95.  Gravel. 

Stony  loams — soils  containing  large  numbers  of  stones  over  one  inch 
in  diameter. 

98.  Stony  loam. 

Rock  Outcrop. 

The  complete  type  number  may  be  formed  in  each  by  prefixing 
the  number  of  the  area  or  sub-province  in  which  it  occurs. 

SOIL  SURVEYS. 

In  order  to  make  a  scientific  study  of  soils  and  to  apply  the 
knowledge  to  practical  agriculture,  it  is  very  desirable  that  the 
samples  studied  be  taken  from  areas  that  are  representative  of  more 


SUB-PROVINCES,  CLASSES,  TYPES  AND  SURVEYS        117 

than  a  single  farm.  The  study  of  a  sample  that  is  ordinarily  sent 
in  by  a  farmer  for  analysis  means  little  to  the  agriculture  of  a 
state  or  even  a  county.  The  samples  must  be  taken  from  areas  that 
represent  some  distinct  type  of  soil  and  care  must  be  taken  to  avoid 
errors  due  to  local  variations.  In  order  to  place  the  sampling  and 
analysis  of  soils  upon  a  truly  scientific  basis,  a  soil  survey  in  which 
the  different  types  of  soil  are  located  on  a  map  should  be  made, 
and  the  samples  secured  according  to  the  types  shown  by  the  soil 
map. 

Soils  are  sufficiently  uniform  and  constant  in  texture  to  be 
divided  into  distinct  types  with  fairly  well  defined  boundaries,  and 
a  soil  survey  consists  in  working  out  these  boundaries  in  the  field 
and  locating  them  on  a  map.  The  type  is  the  unit  of  the  soil  sur- 
vey. The  soils  are  examined  to  a  depth  of  40  inches  by  means  of 
an  auger,  and  the  variations  not  only  of  the  surface  but  also  of  sub- 
surface and  subsoil  are  noted.  In  some  cases  where  the  deeper  sub- 
soil is  peculiar  and  affects  drainage,  the  examination  may  extend 
to  a  depth  of  80  inches.  This  applies  especially  where  sand  or 
gravel  subsoils  occur. 

Surveys  in  Different  States. — Some  soil  survey  work  has  been 
carried  on  in  every  state.  It  was  begun  in  1899  and  since  then 
479,059,000  acres,  or  25.2  per  cent  of  area  of  the  United  States,  have 
been  surveyed.  The  soil  survey  of  one  state,  Rhode  Island,  has 
been  completed.  Xearly  all  of  the  work  that  has  been  done  has  been 
in  cooperation  with  the  Bureau  of  Soils,  this  organization  furnishing 
half  the  men  and  their  expenses,  while  the  state  does  an  equal 
amount.  In  a  few  cases,  as  in  Kentucky  and  Illinois,  survey  work 
has  been  done  independently  of  the  Bureau  of  Soils.  In  the  latter 
state,  GO  per  cent  of  the  entire  area  has  been  surveyed. 

1.  Objects  of  a  Soil  Survey. — The  objects  of  a  soil  survey  may 
be  stated  as  follows:  (a)  to  take  an  invoice  of  the  agricultural 
resources  of  a  country,  for  they  depend  first  of  all  upon  the  soils; 
(b)  to  provide  a  scientific  basis  for  consistent  soil  investigation  so 
that  time  may  be  used  to  the  best  advantage  in  studying  the  various 
types  and  problems;  (c)  to  furnish  a  basis  for  intelligent  recom- 
mendations for  permanent  soil  improvement;  (d)  to  give  the  farmer 
who  desires  to  study  and  improve  his  soil  the  information  necessary  ; 
(e)  in  many  counties  to  give  to  the  county  agriculturist  a  valuable 
asset  to  aid  in  his  work  ;  and  (f )  to  give  a  basis  for  the  introduction 
of  new  crops  or  farm  practices.  If  the  work  ceases  with  the  mapping 


118  SOIL  PHYSICS  AND  MANAGEMENT 

of  the  soils,  very  little  of  real  value  is  accomplished,  as  the  soil 
survey  is  only  preliminary  to  a  more  complete  investigation.  If, 
however,  the  soils  are  analyzed,  field  experiments  carried  on,  reports 
published  giving  the  results  of  the  work,  and  recommendations  for 
improvement  and  management  made,  the  farmer  may  avail  himself 
of  all  this  information  for  improving  his  soil  and  his  farm  manage- 
ment generally. 

2.  Methods  of  the  Survey. — For  the  application  of  this  infor- 
mation to  the  individual  farm,  it  is  necessary  that  the  maps  showing 
the  soils  of  the  farm  should  he  accurate  in  all  details.  To  accom- 
plish this,  three  things  at  least  are  necessary:  first,  careful,  well- 
trained  men  to  do  the  work;  second,  an  accurate  hase  map  upon 
which  to  show  the  results  of  their  work ;  and  third,  the  means  nec- 
essary to  enable  the  men  to  place  the  soil  type  boundaries,  streams, 
etc.,  accurately  upon  the  map. 

For  work  in  the  field  each  man  must  be  familiar  with  the  soil 
types  and  their  variations  in  the  area  he  is  surveying;  he  carries 
an  auger  for  examining  the  soil  to  a  depth  of  40  inches,  a  map  of 
the  area  made  to  the  proper  scale  mounted  upon  a  small,  smooth, 
light  board.  Where  a  satisfactory  base  map  is  not  available,  one 
must  be  made  before  the  mapping  is  begun  or  as  the  work  pro- 
gresses. A  compass  is  carried  to  enable  him  to  keep  his  directions, 
and  he  should  be  an  expert  at  pacing  distances  and  keeping  his  lo- 
cation. The  mapper  should  have  pencils  for  drawing  in  soil  boun- 
daries and  other  features,  and  coloring  soil  areas.  A  traverse  plane 
table  should  be  within  easy  reach  to  be  used  for  getting  the  direc- 
tion of  roads  and  railroads.  If  buggies  are  employed  the  odometer 
may  be  used  for  measuring  distances  along  roads  or  the  revolutions 
of  the  wheel  may  be  counted. 

The  party  consists  of  two  men  who  work  side  by  side.  It  has 
been  found  necessary,  in  order  to  get  the  detail  with  sufficient  ac- 
curacy, that  all  areas  must  be  traversed  and  every  ten  acres  in- 
spected. To  facilitate  this,  each  section  on  the  map  used  is  divided 
into  40-acre  plots  and  these  form  the  most  convenient  unit  area  for 
work. 

Certain  lines  are  selected  that  form  the  center  of  the  work,  such 
as  a  section  line  in  one  case  and  a  half  section  line  in  the  other,  and 
each  man  works  an  area  one-half  mile  in  width,  inspecting  the  soil, 
locating  r.nd  indicating  on  his  map  the  soil  boundaries,  roads, 
streams,  railroads  and  any  other  features  that  should  be  shown. 


SUB-PROVINCES,  CLASSES,  TYPES  AND  SURVEYS        119 


Fio.  f>4. — Soil  Samplers:  (1)  ono-inrh  field  auger;  (2)  one  and  one-half  inch  sampling 
auger;  (3)  rods  for  extension  of  auger  for  examining  deep  subsoil;  (4)  King  sampling  tube, 
(5)  hammer  fur  forcing  tube  into  soil  and  bar  for  lifting  it  out  again. 


120 


SOIL  PHYSICS  AND  MANAGEMENT 


In  some  cases  areas  of  five  acres  or  even  less  are  shown,  but  only 
when  the  area  is  a  very  distinct  type.  In  states  where  no  land 
surveys  have  been  made  the  roads  form  convenient  lines  from  which 
to  work. 

3.  Sampling  of  Soils. — In.  collecting  soil  samples  for  analysis 
each  investigator  has  used  his  own  method.  Uniformity  is  very  de- 
sirable for  purposes  of  comparison.  Since  the  samples  are  to  be  the 
basis  of  investigations  and  plans  for  soil  improvement,  it  is  highly 
important  that  they  should  be  representative  of  their  respective  area 
or  type.  Whatever  the  stratum  divisions  made,  they  should  be  se- 
cured without  mixing  or  contamination  in  any  way.  Various  de- 
vices have  been  used,  but  the  soil  auger  (Fig.  64),  40  inches  long, 
seems  best  for  the  purpose  in  humid  climates. 

The  total  depth  to  which  the  sample  is  taken  varies  with  the 

Weight  of  Soil^trata 


Pounds  per  acre 

Thickness,  inches 

Sands 

Peats 

Clays,  clay 
loams,  silt 
loams,  loam 
and  sandy 
loams 

A 
6/4  Surface  

2,500,000 
5,000,000 

7,500,000 

1,000,000 

2,000,000 
3,000,000 

2,000,000 

4,000,000 
6,000,000 

i 

13^  Subsurface  

20     Subsoil  

V 

SUB-PROVINCES,  CLASSES,  SOILS  AND  TYPES  121 

character  of  the  soil  and  purpose  for  which  it  is  collected.  In  arid 
regions  sampling  is  frequently  done  to  a  depth  of  10  feet,  especially 
for  moisture  determinations,  while  in  humid  regions  40  inches  is 
sufficient.  The  divisions  are  frequently  made  -in  G-,  i)-,  or  12-inch 
depths,  regardless  of  any  natural  divisions  in  the  soil.  At  the 
Illinois  Experiment  Station  the  samples  are  taken  with  a  l1/^- 
inch  auger  to  a  depth  of  40  inches.  The  samples  are  divided  into 
(a)  surface  soil,  G%  inches  in  depth,  about  as  deep  as  plowed, 
and  representing  an  approximate  weight  of  2,000,000  pounds  per 
acre  for  the  common  clays,  clay  loams,  silt  loams,  sandy  loams  and 
loams;  (b)  the  subsurface  stratum,  G%  to  20  inches  in  depth, 
twice  the  thickness  of  the  surface  and  representing  approximately 
a  weight  of  4,000,000  pounds  per  acre;  and  (c)  the  subsoil,  20  to 
40  inches  in  depth  and  weighing  approximately  G. 000, 000  pounds 
per  acre.  Each  of  the  three  samples  is  put  into  a  separate  bag  and 
analyzed  separately. 

Sands  are  the  heaviest  soils  and  peats  and  mucks  are  lightest, 
the  latter  two  being  only  half  as  heavy  as  the  former.  The  weights 
of  the  strata  are  given  in  the  preceding  table. 

These  divisions  do  not  always  represent  the  natural  strata  in  the 
soil,  but  the  depth  of  20  inches  is  usually  near  the  natural  line  of 
change  between  subsurface  and  subsoil,  and  although  there  is  no 
change  at  40  inches  yet  that  is  a  very  convenient  point,  since  it  gives 
the  three  strata  with  a  relative  thickness  of  1,  2,  and  3. 

The  sample  should  be  composite,  and  this  is  much  more  im- 
portant for  the  surface  than  either  of  the  other  strata,  since  it  may 
have  been  modified  more  or  less  by  tillage  or  other  treatment.  At 
the  Illinois  Experiment  Station  the  surface  sample  is  secured  from 
12  to  16  different  borings  at  some  distance  apart,  but  all  from  the 
same  ten  acres.  The  subsurface  and  subsoil  are  secured  from  G  to  8 
different  borings. 

QUESTIONS 

1.  Define  a  sub-province. 

'1.  What  is  the  basis  upon  which  classes  are  made? 

3.  What  factors  are  taken  into  account  in  making  soil  types? 

4.  What  is  the  system   of  soil   nomenclature  as  used   by   the   Bureau  of 

Soils? 

5.  What  is  the  significance  of  color  in  naming  soils? 
0.  How  are  "on'1  and  "  over ''  used  in  naming  soils? 

7.  Define  peats. 

8.  Define  deep,  medium  and  shallow  peat. 

9.  Define  peaty  loams  and  mucks. 


122  SOIL  PHYSICS  AND  MANAGEMENT 

10.  How  do  clays  differ  from  clay  loams  ? 

11.  Distinguish  between  silt  loams  and  loams. 

12.  What  are  the  classes  of  sands? 

13.  Why  should  care  be  exercised  in  the  selection  of  samples  for  study? 

14.  Give  the  objects  of  a  soil  survey. 

15.  Why  should  the  surveyor  examine  the  soils  to  a  depth  of  80  inches? 
10.  What  is  necessary  to  make  the  soil  map  valuable? 

17.  What  apparatus  is  necessary  for  the  soil  surveyor? 

18.  How  are  samples  taken? 

19.  To  what  depth  are  they  taken  and  what  divisions  are  made? 

20.  What  precautions  are  to  be  observed  in  taking  samples? 

21.  What  is  a  composite  sample? 

22.  What  is  the  weight  of  the  strata  of  peat  ?    Of  sand  ? 

REFERENCES 
Soil  Reports,  Illinois  Station. 

Field  Operations  of  the  Bureau  of  Soils,  U.  S.  D.  A. 
Kentucky  Station  Bulletins  102,  193,  194,  195. 

Iowa  Station  Bulletin  82,  1905.     Iowa  Soil  Survey  Report,  No.  1,  1917. 
Soil  Survey  Reports.  Wisconsin  Survey  Bulletins  Nos.  28-40,  1913-14. 
Ohio  Reoonnoissance  Soil  Survey.     Field  Operations  Bureau  of  Soils,  1912. 
Missouri  Station  Research  Bulletin  3,  1910. 

Pennsylvania  Station  Bulletin  132,  Soils  of  Pennsylvania,  1914. 
Michigan  Geological  and  Biological  Survey,  Publication  7,  Geological  Series 

5;  Publication  9,  Geological  Series  7. 
Tennessee  Station  Bulletin,  vol.  x,  No.  3,  1897. 


CHAPTER    X 
MINERAL  CONSTITUENTS 

I.   SOIL  PARTICLES  AND  THEIR  SEPARATION' 

THE  forces  at  work  on  rocks  break  them  down  into  soil  material, 
the  particles  of  which  are  of  various  sizes  and  shapes.  The  relative 
proportion  of  the  different  sizes  is  a  very  important  factor  in  the 
character  of  a  soil.  As  a  general  rule  where  soils  contain  large  per- 
centages of  a  certain  grade  of  particles,  one  or  two  per  cent  makes 
very  little  difference  in  the  physical  phenomena  that  take  place.  It 
is,  however,  of  considerable  importance  to  know  the  approximate 
physical  composition  or  texture,  as  it  usually  gives  some  idea  of  the 
capillary  power,  aeration,  percolation  and  other  properties  of  the 
soil. 

There  are  frequent  exceptions  to  this,  however.  The  physical 
composition  gives  no  idea  of  the  arrangement  of  the  particles  or 
structure  of  the  soil.  The  aggregation  of  the  particles  into  granules 
or  crumbs  plays  a  most  important  part  in  the  physical  phenomena 
that  take  place.  Some  expression  for  showing  this  is  very  desirable. 

Mechanical  or  physical  analysis,  which  is  the  process  of  sepa- 
rating a  soil  into  the  different  grades  of  particles  according  to  size, 
is  an  attempt  to  accomplish  this. 

As  yet,  however,  no  very  scientific  grouping  of  the  soil  particles 
has  been  devised.  That  of  Dr.  Hopkins  is  without  doubt  one  of  the 
best,  as  it  recognizes  a  constant  factor  or  ratio,  the  square  root  of 
ten-  Between  groups.  In  other  methods  or  schemes  the  ratio  be- 
tween grades  varies  quite  widely.  The  result  is  that  when  an 
analysis  is  made  of  soils  of  a  regularly  decreasing  or  increasing  size 
of  particles  no  uniformity  is  shown. 

Several  systems  have  been  devised,  of  which  the  principal  ones 
in  this  country  are  given  in  the  accompanying  table. 

It  will  be  noted  that  in  the  Osborne  system  the  factors  vary  from 
2  to  /> ;  in  the  Bureau  of  Soils  from  2  to  10;  in  Hilgnrd's  from  1.:> 
to  3  ;  in  the  Hopkins  system  the  constant  factor  is  3.1G  or  the  square 
root  of  10. 

123 


124 


SOIL  PHYSICS  AND  MANAGEMENT 


Different  Systems  of  Physical  Analysis,  with  the  Grades  and  Ratio  or  Factor 

Between  Grades l 


Osborne 

Hopkins 

Bureau  of  Soils 

Hilgard 

Number 

Grades 

Factor 

Grades 

Factor 

Grades 

Factor 

Grades 

Factor 

of  group 

mm. 

mm. 

mm. 

mm. 

1 

3.000 

1.0000 

2.000 

3.000 

2 

1.000 

3 

0.3160 

3.16 

1.000 

2 

1.000 

3 

3 

.500 

2 

0.1000 

3.16 

0.500 

2 

0.500 

2 

4 

.250 

2 

0.0316 

3.16 

0.250 

2 

0.300 

1.6.6 

5 

.050 

5 

0.0100 

3.16 

0.100 

2.5 

0.160 

1.87 

6 

.010 

5 

0.00316 

3.16 

0.050 

5 

0.120 

1.33 

7 

0.0010 

3.16 

0.005 

10 

0.072 

1.65 

8 

0.047 

1.53 

9 

0.036 

1.30 

10 

• 

0.025 

1.44 

11 

0.016 

1.56 

12 

0.010 

1.6 

1.  Methods  of  Mechanical  or  Physical  Analysis. —  (a)  The 
Sieve  Method. — The  sieve  method  is  used  as  a  part  of  practically 
every  system  for  the  separation  of  gravel  and  some  or  all  grades 
of  sand.  It  consists  of  using  sieves  with  openings  of  the  required 
size  for  making  the  necessary  separation.  The  separations  may 
be  made  dry  or  by.  washing  the  material  through  with  water.  The 
latter  is  preferable. 

(b)  The   Subsidence  Method. — The  soil   to  be  analyzed  is 
thoroughly  disintegrated  by  shaking  with  water  containing  a  few 
drops  of  ammonia.     It  is  then  passed  through  a  battery  of  sieves 
to  remove  the  sand  and  gravel.    The  water  with  the  fine  material  in 
suspension  is  then  placed  in  a  wide-mouthed  bottle  and  the  finer 
grades  are  decanted  first.    This  is  accomplished  by  filling  the  bottle 
such  as  shown  in  figure  G5  to  a  certain  mark  with  water  and  allow- 
ing it  to  stand  sufficiently  long  for  the  coarser  grades  to  settle  below 
the  mouth  of  the  tube.     The  supernatant  liquid  with  its  grade  of 
soil  particles  is  then  blown  off  through  the  tube  B  by  forcing  air 
through  the  tube  A.     The  contents  of  the  bottle  are  stirred  and 
sufficient  time  is  allowed  for  the  coarser  particles  to  subside  again. 
As  the  sands  tend  to  carry  the  fine  material  down  with  them  this 
operation  must  be  repeated  several  times.    The  same  thing  is  done 
for  each  of  the  other  grades.    The  microscope  is  used  to  determine 
whether  the  proper  size  is  being  removed.     The  great  amount  of 
time  required  is  a  serious  objection  to  this  method. 

(c)  Schone's  Elutriator  Method.2 — The  method  of  separating 
soil  particles  by  currents  of  water  of  varying  velocities  was  first 


MINERAL  CONSTITUENTS 


125 


applied  by  Nobel  in  his  apparatus  given  in  figure  66.  This  was  not 
very  satisfactory  and  the  same  principle  was  applied  somewhat  dif- 
ferently by  Scheme  in  his  elutriator.  The  apparatus  consists  of  a 
conical  glass  tube,  as  shown  in  figure  67.  The  sample,  after 
thorough  disintegration  and  passing  through  sieves  to  remove,  the 
coarser  material,  is  placed  in  the  tube  and  a  current  of  water  allowed 


Fio.  65. — Bottle  for  Subsidence  Method  of  mechanical  analysis.  By  forcing  air  into  the 
bottle  through  A,  the  water  with  the  suspended  particles  ia  forced  out  through  B  to  the  level 
of  C. 

to  enter  at  G.  It  is  evident  that  the  size  of  the  particles  carried 
upward  and  through  the  outlet  tube  will  depend  upon  the  rate  of 
flow  of  the  water,  and  by  regulating  this  the  separations  are  made. 
There  are  some  inaccuracies  in  this  method  caused  by  counter-cur- 
rents in  the  elutriation  cylinder  and  the  tendency  of  the  particles 
to  collect  into  grannies.  In  order  to  overcome  this,  Hilgard  devised 
his  churn  elutriator. 


126 


SOIL  PHYSICS  AND  MANAGEMENT 


(d)  The  Churn  Elutriator  Method  of  Hilgard.3— This  con- 
sists of  an  apparatus  as  shown  in  figure  68.  The  soil  in  suspension  is 
placed  in  the  hase  of  a  cylindrical  tuhe  which  contains  a  rapidly  re- 
volving stirrer.  Water  is  forced  into  the  base  of  the  tuhe  in 
amounts  sufficient  to  create  an  upward  current  just  rapid  enough  to 
carry  out  the  finest  particles.  When  these  are  removed  the  rate  of 


FIG.  66. 


FIG.  67. 


FIG.  68. 


Fio.  66. — Nobel's   Elutriatpr.     The   suspended   soil   is   placed   in    C  and   allowed  to   flow 

through  the  conical  glasses  1,  2,  3,  and  4,  giving  five  different  grades. 

Fio.  67. — Schone's  Elutriator.  The  water  enters  at  G  and  the  grades  are  collected  at  A". 
Fio.  68.— Hilgard's  Churn  Elutriator. 

the  current  is  increased  and  another  grade  is  carried  out.  A  screen 
between  the  stirrer  and  the  separating  chamber  prevents  the  agita- 
tion of  water  in  this  chamber.  In  this  way  all  separations  except  the 
finest  particles  are  made.  Particles  of  clay  less  than  0.0023  mm. 
must  be  separated  by  subsidence.  This  is  done  by  allowing  the 
larger  particles  to  subside  for  24  hours  and  then  decanting  the  clay. 


MINERAL  CONSTITUENTS 


127 


(e)  Centrifugal  Method.4 — The  centrifugal  method  lias  been 
perfected  by  the  Bureau  of  Soils  and  is  now  used  more  extensively 
in  this  country  than  any  other.  The  machine  for  this  purpose  is 
shown  in  figure  GO.  It  consists  of  a  centrifuge  suspended  from  the 


FIG.  09.  —  Machine  for  centrifugal  analysis  of  soils.     Bureau  of  Soils,  U.  S.  D.  A. 


Fio.  70. — Voder's  Centrifugal  Elutriator. 

shaft  of  an  electric  motor.  The  sample  to  he  analy/ed  is  detloceu- 
lated  by  shaking  with  water  containing  a  few  drops  of  ammonia. 
This  requires  from  two  to  thirty  hours.  The  clay  and  silt  are  sepa- 
rated from  the  sands  by  subsidence  and  dccantation  or  bv  sieves. 


128 


SOIL  PHYSICS  AND  MANAGEMENT 


The  water  containing  the  silt  and  clay  is  put  in  test  tubes  and 
whirled  at  a  speed  of  about  1000  revolutions  per  minute.  The  time 
necessary  to  throw  down  the  silt  is  determined  by  microscopic  exami- 
nation of  the  material  in  suspension.  After  decanting  the  clay  re- 
maining in  suspension,  the  test  tube  is  filled  with  water,  the  sediment 
is  stirred  and  the  operation  repeated  until  the  clay  is  all  removed. 
By  running  the  centrifuge  at  a  slower  rate  or  shorter  time  another 
grade  may  be  left  in  suspension  and  decanted. 

(f)  Voder's  Centrifugal  Elutriator.5 — One  of  the  best  ma- 

chines for  physical  analysis  is 
Yoder's,  in  which  he  has  com- 
bined the  principles  of  the  cen- 
trifuge and  the  elutriator,  as 
shown  in  figure  70.  The  par- 
ticles are  subjected  to  two  forces, 
the  centrifugal  tending  to  throw 
them  down  and  the  hydraulic 
carrying  them  upward.  The 
centrifugal  effect  is  exerted  to  a 
greater  extent  upon  the  -coarser 
particles  and  the  hydraulic  upon 
the  finer.  By  this  combination 
a  more  rapid  separation  may  be 
accomplished.  The  apparatus 
consists  of  an  elutriating  bottle, 
B,  into  which  the  suspended  soil 

FIG.  7i.— King's  aspirator  for  the  determi-  is  placed  after  the  sands  are  re- 
nation  of  the  effective  diameter  of  soil  parti-  moved.      Water  enters  at  F,  and 

the  overflow  with  the  sediment 

is  collected  in  the  tube  T.  While  it  does  its  work  very  thoroughly 
and  quickly,  it  is  a  very  expensive  and  a  rather  delicate  piece  of 
apparatus. 

(g)  King's  Aspirator  Method.6 — King  was  of  the  opinion  that 
ordinary  mechanical  analyses  do  not  furnish  a  basis  for  determining 
any  very  important  data  for  soils.    The  arrangement  of  the  particles 
into  groups  is  of  much  consequence  in  physical  phenomena,  but 
mechanical  analysis  does  not  indicate  the  structure.     In  'order  to 
overcome  this  difficulty  he  worked  out  the  method  for  finding  the 
"  effective  diameter  "  of  soil  particles.     The  grouping  of  particles 
upon  which  the  percolation  of  air  and  water  and  other  phenomena 
depends  is  taken  into  account.    The  rate  at  which  air  passes  through 
a  column  of  air-dried  soil  of  a  given  cross  section  and  length  under 


o 


MINERAL  CONSTITUENTS 


129 


standard  conditions  of  temperature  and  pressure  gives  the  data  by 
which  the  diameter  is  determined.  The  soil  is  placed  in  D,  figure 
71,  a  tube  having  a  capacity  of  100  or  200  c.c.  with  a  wire  gauze 
bottom.  This  is  connected  by  means  of  a  tube  to  the  aspirator  A. 
A  cord  with  a  weight  attached  exerts  sufficient  "  pull  "  to  draw  the 
air  through  the  soil.  The  "effective  diameter"  is  deduced  by 
means  of  a  formula  using  the  data  determined.  The  flow  of  water 
through  the  soil  computed  from  the  "effective  diameter"  obtained 
corresponds  very  closely  to  that  actually  observed,  as  shown  in  the 
table. 

Comparison  Between  Computed  and  Observed  Flow  of  Water 


Grade  of  sand 

Effective  diameter 
of  particles 

Computed  flow  of 
water 

Observed  flow  of 
water 

mm. 

Gms. 

Gms. 

8 
7 
6 

2.54 
1.808 
1.451 

2,277 
1,132 
757 

2,296 
1,090 
756 

5V£ 

1.217 

522 

542 

5 

1.095 

453.2 

504.6 

4 

.9149 

297.5 

329.2 

3 

.7988 

193 

210.0 

2 

.7146 

122 

138.6 

1 

.6006 

80.6 

94.8 

0 

.5169 

66.8 

72.3 

II.  MINERAL  SOIL   CONSTITUENTS  AND  THEIR  PROPERTIES 

1.  Colloids. — While  the  colloids  of  soils  are  usually  classed 
along  with  clay,  their  importance  justifies  separate  treatment.  Al- 
though not  as  abundant  in  soils  as  many  other  constituents,  yet 
they  possess  such  distinctive  characteristics  and  impart  these  so 
noticeably  that  they  are  of  the  greatest  consequence  not  only  from 
a  physical  standpoint  but  from  a  chemical  and  biological  as  well. 
Xon-colloids  are  called  crystalloids. 

Colloids  are  substances  composed  of  the  very  finest  of  particles 
and  when  mixed  with  water  appear  to  go  into  solution.  When  con- 
taining a  certain  amount  of  water  they  appear  jelly-like  or  gelati- 
nous. Since  the  colloidal  state  is  dependent  upon  the  sixe  of  parti- 
cles, it  follows  that  many  substances  may  exist  in  both  colloidal  and 
crystalloidal  forms.  Up  to  the  present  time  only  about  -100  sub- 
stances have  been  found  that  exist  in  both. 

Examples  of  Colloids. — The  word  colloid  is  derived  from  rolJa, 
meaning  glue.  A  glue  or  jelly-like  consistency  is  one  of  the  most 
familiar  characteristics  of  colloids.  In  the  inorganic  world  almost 
9 


130  SOIL  PHYSICS  AND  MANAGEMENT 

all  metals  and  metalloids  have  beeii  produced  in  a  colloidal  state. 
The  simplest  compounds  of  these,  as  oxides,  sulfides,  chlorides, 
hydroxides,  some  carbonates,  chromates,  phosphates,  sulfates,  and 
silicates,  occur  in  this  form.  Among  the  organic  substances  that 
occur  as  colloids  are  starch,  dextrin,  gum,  rubber,  glue,  gelatine, 
caseins,  albumins,  humus,  and  proteins  in  general. 

Properties  of  Colloids. — The  difference  between  colloids  and 
crystalloids  in  one  of  physics  and  not  of  chemistry.  The  chemical 
composition  is  the  same  in  whichever  state  they  occur.  Hence,  a 
study  of  colloids  is  largely  a  study  of  their  physical  properties  and 
characteristics. 

(a)  Size  of  Particles. — The  upper  limit  of  size  for  colloids  is 
near  the  limit  of  visibility  with  the  ordinary  high-power  microscope, 
which  is  not  far  from  0.0001  mm.    With  the  most  powerful  micro- 
scope some  of  the  largest  colloidal  particles  may  be  seen ;  with  the 
ultra-microscope,  particles  0.000005  mm.  in  diameter  are  about  the 
limit  of  visibility.    Many  smaller  particles  exist,  but  their  presence 
is  revealed  only  by  the  properties  of  their  suspensions.    The  parti- 
cles larger  than  0.0001  mm.  give  ordinary  suspension  and  may  some- 
times show  some  properties  of  colloids.     Those  between  the  above 
size  and  the  molecule  give  colloidal  suspensions,  while  the  molecules 
give  true  solutions. 

The  smaller  the  particle  the  longer  it  will  remain  in  suspension. 
This  is  due  to  the  fact  that  the  specific  gravity  of  the  particle  and 
its  adhering  film  of  water  have  such  a  low  specific  gravity  that  it 
varies  but  little  from  that  of  water  (see  page  35). 

(b)  Brownian  Movement. — Very  fine  particles  in  water  are  con- 
stantly in  motion.    This  movement  is  not  a  definite  progressive  one, 
but  an  irregular,  jerky  motion  from  one  side  to  the  other.    Particles 
as  large  as  0.01  mm.  sometimes  show  a  slow  movement  of  this  kind, 
but  it  is  best  developed  in  the  very  finest  particles.    The  movement 
is  increased  by  higher  temperature. 

(c)  Dialysis. — Dialysis  is  the  diffusion  of  a  substance  through 
a  membrane.    Experiments  show  that  colloids  will  not  pass  through 
membranes  or  at  best  only  very  slowly.    Separation  of  colloids  from 
crystalloids  may  be  made  in  this  way. 

From  the  following  table  it  will  be  seen  that  dialysis  takes  place 
about  80  times  as  rapidly  with  crystalloids  as  with  colloids.  This 
is  due  to  the  fact  that  the  parchment  itself  is  a  colloid. 

(d)  Diffusion. — Colloids  diffuse  very  slowly  and  they  do  not 
allow  other  colloids  to  pass  into  them.    Crystalloids  may  pass  into 


MINERAL  CONSTITUENTS  131 

or  through  them  quite  readily.  Because  of  this  lack  of  power  to 
diffuse,  colloids  possess  very  little  osmotic  pressure.  Pfell'er  gives 
the  osmotic  pressure  of  a  one  per  cent  solution  of  sugar  as  equiva- 
lent to  a  column  of  mercury  51.8  cm.  high,  while  that  of  a  one  per 

Dialysis  and  Diffusion  of  Colloids  and  Crystalloids 


Substances 


Crystalloids 

Sodium  chloride 1 .00 

Ammonia 0.85 

Alcohol j  0.47  2.0 

Glucose. . ,  0.36  3.0 


1.0 
0.0 


Cane  sugar. 


0.47 


Average ;      0.63 


3.0 

1.92 


Colloids 
Gum  arabic.  .      .         

O.OOS 

7.0 

Tannin  

0.015 

11.0 

Albumin  

0.003 

21.0 

Caramel  

0.005 

42.0 

Averaee.  .  . 

0.00775 

20.25 

cent  of  gum  is  only  (>.!)  cm.     From  the  above  table  it  will  be  seen  that 
crystalloids  diffuse  over  ten  times  as  rapidly  as  colloids. 

(e)  Freezing  and  lioiling  Point*. — The  lowering  of  the  free/ ing 
and  boiling  points  by  crystalloids  such  as  common  salt  in  solution 
is  familiar  to  every  one.     The  change  in  these  is  in  proportion  to 
the  amount  dissolved.     Colloids  have  very  little  effect.     Forty-four 
grams  of  protein  dissolved  in  100  grams  of  water  lowered  the  free/- 
ing point  only  0.06°  C.7 

(f)  Electrical  Behavior. — Colloids  are  poor  conductors  of  elec- 
tricity as  compared  with  crystalloids,  and  their  conductivity  de- 
creases with  the  amount  of  colloid  in  the  disperse  medium.     Any 
substance  in  contact  with  water  and  many  other  liquids  acquires  an 
electric  charge.    ^lost  substances  become  negatively  charged  in  con- 
tact with  water.     The  charge  can  be  varied  and  even  reversed  by 
electrolytes  and  may  even  become  zero  at  certain  suitable  concen- 
trations.   If  a  current  of  electricity  is  passed  into  a  colloidal  solu- 
tion, the  particles  migrate  to  one  pole  or  the  other.     If  they  miirrate 
to  the  negative  pole  (cathode)  they  are  positive,  and  if  toward  the 
positive  pole  (anode)  they  are  negative.     The  colloidal  condition 


132  SOIL  PHYSICS  AND  MANAGEMENT 

exists  as  long  as  the  charge  is  the  same.  This  condition  is  not  con- 
fined to  colloidal  particles  alone,  but  to  coarser  material  in  sus- 
pension. 

If  an  electrolyte  is  added  to  the  solution  and  the  ions  and 
particles  carry  opposite  electric  charges,  floccules,  are  formed  which 
settle  to  the  bottom.  If  the  ions  and  colloidal  particles  have  the  same 
electric  charges  the  colloidal  condition  is  maintained.  If  two  col- 
loids of  opposite  charges  are  brought  together,  mutual  precipitation 
will  take  place,  and  if  they  are  the  same  their  stability  will  be  in- 
creased. In  adding  an  electrolyte  to  completely  precipitate  a  colloid 
a  sufficient  amount  must  be  added  so  that  the  charge  of  one  exactly 
neutralizes  the  charge  of  the  other. 

(g)  Adsorption. — Adsorption  is  a  surface  phenomenon  and 
hence  any  increase  in  the  total  amount  of  surface  area  will  increase 
the  adsorption.  Colloids  possess  this  property  to  a  high  degree  be- 
cause of  the  large  total  area  of  the  small  particles.  When  a  solid 
is  exposed  to  a  gas  a  certain  amount  of  gas  adsorption  occurs.  When 
a  solid  and  a  liquid  come  in  contact,  concentration  occurs  on  the  in- 
terface between  the  two.  This  concentration  is  known  as  adsorp- 
tion. All  substances  are  not  equally  adsorbed  by  colloids.  The 
same  is  true  of  all  ions.  If  potassium  chloride  is  passed  through  a 
soil  more  of  the  potassium  ions  will  be  adsorbed  than  of  the  chlorine. 

(h)  Shrinkage. — The  property  of  shrinkage  is  very  character- 
istic of  cololids  (see  Fig.  72). 

Colloids  in  Soils. — The  -colloids  in  soils  consist  of  both  organic 
and  inorganic  or  mineral  substances. 

(a)  Organic  Colloids. — Some  of  the  various  forms  of  humus 
constitute  the  organic  colloids  and  probably  form  the  larger  part 
of  colloids  in  many  soils.     These  are  formed  as  a  result  of  bac- 
terial action  in  the  process  of  humification.     Part  of  the  organic 
matter  is  broken  down  into  such  minute  particles  as  to  form  colloids. 
The  amount  is  constantly  changing  in  the  same  soil.    Since  granu- 
lation takes  place  more  perfectly  in  the  spring  than  at  any  other 
time  of  the  year,  it  would  seem  that  there  is  a  greater  supply  in  the 
soil  at  this  time  than  at  other  periods.    This  may  apply  to  mineral 
colloids  as  well.    The  adsorptive  power  of  these  organic  colloids  for 
water  is  of  great  economic  importance  in  soils.     Schlossing  states 
that  one  per  cent  of  calcic  humate  (colloidal)  has  as  much  cement- 
ing power  as  11  per  cent  of  plastic  clay. 

(b)  Mineral  Colloids. — Mineral  colloids  are  found  most  abun- 
dantly in  fine-grained  soils  such  as  clays  and  clay  loams.    The  col- 


MINERAL  CONSTITUENTS 


133 


134  SOIL  PHYSICS  AND  MANAGEMENT 

loids  consist  largely  of  ferric  oxide,  ferric  hydrate,  silicic  acid  and 
hydra  ted  aluminum  silicate.  These  are- formed  in  the  decomposition 
of  rocks.  In  the  decomposition  of  most  feldspars  the  silicic  acid 
and  aluminum  silicate  are  formed,  but  not  all  in  a  colloidal  state. 
Zeolites  easily  give  rise  to  colloidal  silica.  While  many  substances 
exist  in  a  colloidal  state  in  soils,  yet  the  total  amount  is  not  large. 
Warrington  estimates  it  at  never  over  two  per  cent. 

2.  Clays  and  Clay  Loams. — Mineralogically  clay  is  com- 
posed largely  of  kaolinite,  a  hydrous  aluminum  silicate  that  is 
formed  from  decomposition  of  aluminous  minerals.  In  addition,  it 
may  contain  very  finely  divided  particles  of  quartz,  feldspar  or  other 
minerals.  In  fact,  clay  may  be  composed  entirely  of  other 
minerals  than  kaolinite,  although  th;s  is  not  usually  the  case. 
Physically,  clay  consists  of  particles  less  than  0.001  mm.  in  diameter 
(Hopkins),  0.005  mm.  (Bureau  of  Soils)  or  0.0023  mm.  (Hilgard) 
(see  table  on  page  124).  This  is  divided  into  two  parts,  which  may 
be  called  clay  proper,  consisting  of  particles  large  enough  to  be  dis- 
tinguished with  the  microscope,  about  0.0001  mm.  in  diameter,  and 
a  small  amount  of  hydrous  aluminum  silicate  whose  particles  are 
very  small  and  constitute  part  of  the  mineral  colloids. 

(a)  Tenacity. — Tenacity  is  that  quality  of  cohesiveness  by 
which  substances  resist  disruption,  imparting  more  or  less  stability 
to  them.  In  soils  this  property  is  due  primarily  to  colloids.  Clays 
and  clay  loams,  however,  possess  this  property  to  a  high  degree. 
Soils  have  been  divided  according  to  their  tenacity  into  "heavy" 
and  "  light."  A  "  light "  soil  is  one  that  works  easily,  as  sand  or 
peat,  and  incidentally  has  a  high  specific  gravity,  as  sand,  or  a  low 
specific  gravity,  as  peat,  but  all  possessing  very  little  cohesiveness. 
"  Heavy  "  soils,  on  the  other  hand,  are  those  containing  a  great  deal 
of  clay,  and  hence  possessing  a  high  tenacity.  Clays,  clay  loams, 
and  heavy  silt  loams  and  some  sandy  loams  are  examples  of  these.  In 
absolute  weight  they  are  not  as  heavy  as  the  sand  soils,  but  the 
greater  tenacity  possessed  by  them  makes  them  more  difficult  to 
plow.  Hence  the  term  "  heavy  "  is  applied  to  them. 

A  high  moisture  content  decreases  tenacity.  However,  a  medium 
amount  of  moisture  imparts  a  high  degree,  as  does  also  an  extremely 
small  amount  of  moisture,  as  where  the  soil  becomes  dry  and  cloddy. 
This  is  due  to  the  hardening  of  colloids  and  the  deposition  of  soluble 
salts  as  a  cementing  material  between  the  soil  particle*.  The  tenac- 
ity of  "  heavy "  soils  may  be  diminished  by  the  addition  of  or- 


MINERAL  CONSTITUENTS 


135 


game  matter,  and  in  general  by  anything,  as  lime,  that  will  produce 
granulation. 

(b)  Shrinkage. — Clay  possesses  the  property  of  shrinkage  to  a 
remarkable  degree,  due  to  the  loss  of  moisture  from  the  particles 
in  general  but  the  colloidal  constituent  particularly.  This  shrinkage 
is  emphasized  when  a  large  amount  of  humus  is  present,  because 
the  humus  is  partly  colloidal.  Clay  has  been  found  to  shrink  31.9 
per  cent,  and  peat  32. (J  per  cent  (see  accompanying  table).  Hence 
a  soil  composed  of  both  of  these  will  possess  the  property  of  shrink- 
age to  a  great  and  sometimes  injurious  degree. 

Shrinkage  of  Soils  of  Varied  Physical  Composition,  with  the  Moisture  and 
Organic-Mattel  Content  8 


Soils 

Total 
organic  matter 

Moisture 

A  real 
shrinkage 

Sand  

per  cent 

0.75 

per  cent 

9.67 

per  cent 

1.88 

Yellow  fine  sandy  loam 

0.80 

21.39 

2.48 

Brown  sandy  loam  

2.90 

17.43 

4.94 

White  silt  loam  

0.79 

23.69 

4.11 

Brown  silt  loam              .                  .  . 

4.88 

31.93 

10.26 

Black  clay  loam 

5.50 

40.83 

19.00 

Drab  clay  

3.60 

61.94 

31.93 

Peat  .                                             .... 

64.40 

193.94 

32.64 

This  property  is  frequently  detrimental  to  crops,  because  of  the 
formation  of  large  cracks  that  tear  the  roots  of  the  plants  as  well  as 
cause  excessive  loss  of  moisture  (Figs.  72  and  73).  The  property  of 
shrinkage  is  a  primary  cause  of  granulation,  and  this  is  only  pos- 
sessed by  soils  which  contain  colloids.  It  is  also  an  aid  to  percola- 
tion and  drainage,  because  the  cracks  produced  by  shrinkage  do  not 
close  entirely,  thus  leaving  passageways  for  water.  During  the 
dry  summer  of  1914,  a  clay  loam  shrank  to  such  an  extent  that  an 
inch  auger  could  be  pushed  into  cracks  without  any  effort  to  a  depth 
of  24  to  28  inches.  The  cracks  undoubtedly  extended  to  a  depth 
of  30  inches. 

(c)  Plasticity. — A  moist  clayey  soil  may  be  molded  into  any 
form  or  pressed  into  thin  plates,  retaining  the  shape  indefinitely. 
The  property  permitting  this  is  called  plasticity.  The  degree  of 
plasticity  varies  directly  as  the  amount  of  colloids  present.  Tf  is  not 
a  desirable  quality  for  soils  to  possess,  ns  such  are  liable  to  be  more 
readily  puddled.  The  amounts  of  shrinkage,  hygroscopic  water  and 
adsorption  are  approximate  indications  of  the  plasticity  of  day  soils. 


136 


SOIL  PHYSICS  AND  MANAGEMENT 


Highly  plastic  soils  become  very  hard  upon  drying.  Plasticity  may 
be  diminished  by  organic  matter,  granulation  or  change  of  texture. 
Plasticity  may  be  increased  by  the  breaking  down  of  soil  gran- 
ules into  their  individual  soil  particles.  While  this  is  detrimental  to 
soils,  it  is  of  decided  advantage  to  the  ceramist. 

(d)  Puddling. — Clays  and  clay  loams  are  usually  made  up  of 
crumbs  or  granules,  composed  of  many  soil  particles  united  by  a 
weak  cementing  substance,  such  as  humus  or  some  other  colloid.  If 

the  soil  is  worked  or  trampled 
by  stock  when  wet  these  granules 
are  broken  down,  the  colloids  be- 
come somewhat  uniformly  dis- 
tributed throughout  the  mass 
and  an  impervious  condition  re- 
sults. The  soil  is  puddled. 
Water  or  air  will  not  penetrate 
it  and  a  worse  condition  could 
not  well  be  produced.  The  pres- 
ence of  sodium  carbonate  or 
black  alkali,  or  the  long-con- 
tinued application  of  certain 
fertilizers,  such  as  ammonium 
sulfate  or  sodium  nitrate,  brings 
about  a  puddled  condition.  Some 
clay  and  clay  loam  soils  are  pud- 
dled naturally.  This  is  likely 
to  be  the  case  if  they  are  strongly 
acid  and  low  in  organic  matter. 
Water  in  a  soil  acts  as  a  lubri- 
Fio.73.-crack8  in  black  clay  loam  after  cant  and  movement  takes  place 
i9i6ng  dry  pcriod'  photo«raPhed  August,  more  readily  between  the  par- 
ticles. It  also  softens  the 

cementing  material  so  that  the  granules  are  easily  broken  down. 
When  the  soil  is  turned  by  the  plow  a  shearing,  slipping  movement 
is  produced  as  it  curves  over  the  mold  board.  This  will  pulverize  it 
if  in  good  condition,  but  puddle  it  more  or  less  if  wet.  When  a 
heavy  animal  steps  on  the  dry  soil  it  is  compacted,  but  if  wet  the 
foot  sinks  into  the  soil,  causing  a  movement  which  breaks  down 
many  granules,  thus  puddling  the  soil. 

When  puddling  is  produced  in  a  heavy  soil  it  may  be  almost 
worthless  for  a  time,  but  the  natural  agencies  of  freezing  and  thaw- 


MINERAL  CONSTITUENTS  137 

ing  and  wetting  and  drying  will  gradually  restore  the  soil  to  its 
granular  condition.  The  time  required  for  this  depends  somewhat 
upon  the  organic  matter  and  lime  content  of  the  soil.  It  is  never  a 
wise  plan  to  permit  stock  to  run  on  a  moderately  heavy  soil  when 
wet  so  late  in  spring  that  its  granular  condition  will  not  be  restored 
again  by  freezing  and  thawing.  In  the  corn  belt  considerable  dam- 
age is  done  to  the  soil  by  pasturing  the  cornstalks  too  late  in  the 
spring. 

(e)  Coagulation  or  Flocculation. — The  examination  of  a  clay 
soil  usually  shows  it  to  be  made  up  of  fine  particles  cemented  into 
granules,  crumbs,  or  grains.  If  a  few  grains  of  clay  soil  be  pul- 
verized and  put  into  a  liter  of  water  and  stirred  and  allowed  to 
stand  for  several  weeks,  some  material  will  be  found  still  in  suspen- 
sion. If  some  mineral  acids  or  certain  salts  or  lime  water  are  added 
to  this  liquid  coagulation  will  occur  and  floccules  may  be  seen  form- 
ing, which  gradually  settle  to  the  bottom,  carrying  with  them  the 
suspended  clay  particles.  This  may  be  well  shown  by  putting  a 
drop  of  water  with  suspended  clay  under  the  microscope.  Intro- 
duce a  drop  of  lime  water  under  the  cover  glass.  The  particles  will 
at  once  begin  to  collect  in  groups,  showing  the  formation  of  floccules. 
This  process  takes  place  in  soils  due  to  the  presence  of  certain  sub- 
stances in  solution  in  tlie  soil  moisture  that  act  as  electrolytes.  In 
some  cases,  fertilizers  when  added  produce  this  effect,  and  lime- 
stone, which  gives  rise  to  the  soluble  bicarbonate,  produces  floceula- 
tion.  This  is,  however,  a  slow  process  and  will  not  produce  granula- 
tion as  quickly  as  is  ordinarily  supi>osd,  although  heavy  acid  soils 
are  undoubtedly  benefited  physically  by  the  application  of  lime- 
stone. Common  salt  produces  the  same  effect  and  likewise  many 
other  salts.  Most  alkaline  substances,  however,  deflocculate  clay 
soils  and  produce  a  puddled  condition.  Ammonia  and  most  of  its 
salts  are  good  examples.  The  black  alkali  of  the  West  is  especially 
detrimental  because  of  the  physical  effect  it  has  on  soils  in  producing 
a  puddled,  impervious  condition.  This,  however,  may  be  remedied 
by  the  application  of  gypsum,  calcium  sulfate.  The  injurious  effect 
of  sodium  carbonate  or  black  alkali  is  destroyed  by  this  reaction 
and  sodium  sulfate  and  calcium  carbonate  produced,  the  latter  of 
which  has  a  flocculating  effect  on  the  soil  and  soon  changes  the 
puddled  condition  entirely.  It  has  been  observed  frequently  that  the 
water  of  glacial  streams  is  extremely  muddy,  while  that  coming  from 
limestone  regions  is  characterised  by  clearness.  The  difference  is 
due  to  the  lime  content  of  the  water  from  the  two  sources.  In 


138  SOIL  PHYSICS  AND  MANAGEMENT 

regions  where  limestone  is  absent  and  where  the  sediment  of  streams 
comes  from  acid  soils  the  water  is  rarely  clear.  Even  stock  ponds 
in  regions  of  acid  soils  where  the  water  is  seldom  disturbed  never 
become  clear. 

While  clay  soils  are  difficult  to  manage,  due  to  the  danger  of 
puddling  when  too  wet  and  from  clods  when  too  dry,  yet  with 
proper  care,  drainage,  incorporating  organic  matter  and  maintain- 
ing the  supply  of  limestone,  the  condition  of  these  soils  may  be  im- 
proved so  they  work  fairly  well.  In  addition  to  the  flocculation 
produced  by  the  substances  mentioned  above,  natural  causes  hasten 
it.  Wetting  and  drying,  and  freezing  and  thawing,  will  change  the 
character  of  the  soil  from  a  cloddy  to  a  granular  condition,  or  cause 
it  to  "slake."  The  alternate  expansion  and  contraction  of  the  col- 
loidal material,  whether  of  mineral  or  organic  origin,  tend  to  break 
the  soil  into  granules.  Fall  plowing  is  especially  desirable  on 
"heavy"  soils  that  are  well  drained,  because  of  the  good  tilth 
developed  during  winter  by  these  natural  agencies.  If  a  clay  soil 
becomes  cloddy  it  is  practically  impossible  to  reduce  it  to  a  condition 
of  good  tilth  by  any  mechanical  means,  but  if  freezing  and  thawing 
occur,  or  a  shower  falls,  working  it  under  the  right  moisture  con- 
ditions will  break  the  clods  easily  into  masses  of  granules. 

3.  Silt  and  Silt  Loams. — Silt  is  divided  into  three  classes, 
fine,  medium,  and  coarse,  ranging  in  size  from  0.001  to  0.032 
mm.  in  diameter  (Hopkins),  0.005  to  0.05  m.  (Bureau  of  Soils)  or 
0.01  to  0.07  mm.  (Hilgard) .  The  particles  of  fine  silt  are  sufficiently 
small  to  give  to  soils  properties  somewhat  similar  to  those  of  clay, 
but  without  so  much  danger  of  puddling.  Silt  enables  soils  to 
retain  much  moisture  and  gives  great  capillary  power,  and  hence 
forms  some  of  the  best  soils  for  resisting  drouth.  They  are  suf- 
ficiently coarse,  however,  <to'  permit  of  fair  aeration,  but  not  to  an 
excessive  degree,  as  in  tlae  case  of  sands.  The  silt  loam  soils  cover 
extensive  areas  in  the  middle  west  of  the  United  States  and  owe 
their  origin  to  the  loess. 

They  possess  sufficient  tenacity  to  give  the  necessary  stability, 
but  not  enough  to  cause $h jm  to  work  with  any  great  difficulty.  The 
shrinkage,  however,  is  not  usually  sufficient  to  produce  very  in- 
jurious effects.  Since  granulation  depends  upon  the  amount  of  col- 
loids present,  and  since  organic  matter  as  well  as  clay  may  furnish 
this  constituent,  the  silt  loams  containing  the  largest  amount  of 
organic  matter  granulate  best.  Silt  soils  deficient  in  organic  matter, 
such  as  gray  or  yellow  timber  soils,  show  little  or  no  granulation 


MINERAL  CONSTITUENTS  139 

and  may  be  easily  reduced  to  a  powder  or  dust  made  up  of  indi- 
vidual particles.  These  run  together  badly  with  heavy  rains. 

4.  Sands  and  Sandy  Loams. — Sand  is  divided  into  three 
groups,  line,  medium,  coarse  and  sometimes  very  fine,  varying 
from  0.032  to  1  nun.  in  diameter  (  Hopkins),  ().().")  to  1  mm.  (Bureau 
of  Soils),  or  0.12  to  1  mm.  (Hilgard).  Sand  possesses  very  little 
tenacity,  hence  little  stability.  There  is  usually  great  danger  o[ 
movement  by  the  wind  and  in  many  cases  sand  soils  are  seriously 
damaged  in  this  way,  as  i.s  seen  in  the  "  blow-outs  "  in  sand  areas 
(see  p.  o!)).  This  movement  may  be  prevented  by  incorporating 
organic  matter  which  imparts  sufficient  tenacity  to  hold  the  sand. 
The  fine  and  medium  grades  of  sand  allow  fair  moisture  movement 
both  up  and  down,  but  the  coarse  allows  too  much  percolation,  while 
capillary  movement  is  exceedingly  limited.  It  is  generally  believed 
that  sands  are  very  deficient  in  moisture  and  that  the  "tiring"  of 
corn  on  sandy  lands  is  always  due  to  this  cause.  Often,  however, 
it  is  due  to  a  lack  of  nitrogen,  the  drying  of  the  lower  leaves  being 
produced  by  translocation  of  nitrogen  to  carry  on  further  growth  in 
other  parts  of  the  plant.  This  drying  of  the  leaves  may  be  almost 
entirely  prevented  by  supplying  the  crop  with  the  necessarv  food. 
The  fact  that  sands  do  not  retain  much  moisture  enables  them  to 
warm  up  early  in  the  spring. 

">.  Gravel  and  Gravelly  Loams. — Many  types  of  soil  con- 
tain considerable  percentages  of  gravel.  It  is  of  verv  little  use 
except  that  through  its  extremely  slow  decomposition  it  furnishes 
a  small  amount  of  plant  food.  It  may  form  a  part  of  anv  tvpe  of 
soil,  but  is  more  commonly  associated  with  the  coarser  constituents. 

f>.  Stones. — Stones  are  quite  common  in  many  soils  of  the 
glaciated  and  residual  areas,  but  have  very  little  value  except  to 
modify  temperature  and  conserve  moisture  to  a  slight  extent. 
Their  slow  decomposition  may  provide  a  small  amount  of  plant 
food. 

QUESTIONS 

1.  Wlmt  benefit  is  a  knowledge  of  tlie  physical  composition  of  Boils'? 

2.  What  is  meant  by  mechanical  or  physical  analysis? 

.'?.  Why  is  the  Hopkins  method  considered  superior  to  other-' 

4.  Note  the  different  factors  or  ratios  between  the  grades.     How  much  ,},, 

they  vary? 

f>.  Should  these  factors  be  constant  ?     Why? 

fi.  Tlow  is  the  sieve  method  used  ? 

7.  Explain  how  the  separations  are  made  in  the  subsidence  method? 

8.  What  is  the  principle  of  Schone's  elutriation  method? 


140  SOIL  PHYSICS  AND  MANAGEMENT 

9.  What  advantage  does  Hilgard'a  method  possess  over  Schone'sT 

10.  What  effect  does  whirling  the  sample  in  the  centrifuge  have? 

11.  What  is  the  principle  of  Voder's  machine? 

12.  What  is  the  advantage  of  King's  aspirator? 

13.  Describe  the  method  of  King. 

14.  What  is  the  importance  of  colloids  in  soils? 

15.  What  are  colloids? 

16.  \Vhy  may  substances  be  in  both  colloidal  and  crystalloidal  forms? 

17.  Give  examples  of  inorganic  colloids. 

18.  Give  examples  of  organic  colloids. 

19.  Does   colloidal  condition  depend  upon  physical   condition   or  chemical 

composition  ? 

20.  What  about  the  size  of  particles  in  colloids? 

21.  Why  do  small  particles  remain  in  suspension  so  long? 

22.  What  is  Brownian  movement? 

23.  What  is  dialysis? 

24.  What  difference  in  the  dialysis  between  colloids  and  crystalloids? 

25.  Discuss  diffusion  of  crystalloids  in  comparison  to  colloids. 

26.  WThat  effect  do  colloids  have  upon  the  freezing  and  l>oiling  points  of 

liquids? 

27.  What  is  peculiar  in  the  electrical  behavior  of  colloids? 

28.  What  effect  does  an  electrolyte  have  upon  the  colloids? 

29.  When  will  an  electrolyte  completely  precipitate  clay  in  suspension? 

30.  Wliat  is  adsorption? 

31.  Is  it  uniform  for  all  substances? 

32.  What  are  the  organic  colloids  in  soils? 

33.  W7hat  are  the  mineral  colloids? 

34.  Wrhat  may  be  the  mineral  composition  of  clay  ? 

35.  What  is  tenacity? 

36.  Define  a  "  light  "  soil.        A  "  heavy  "  one. 

37.  What  is  the  effect  of  moisture  on  tenacity? 

38.  How  may  the  tenacity  of  soils  be  diminished  ? 

39.  What  causes  soils  to  shrink? 

40.  What  benefit  is  derived  by  shrinkage?     What  disadvantage? 

41.  Define  plasticity. 

42.  How  may  plasticity  be  increased?    Diminished? 

43.  What  is  the  condition  of  a  puddled  soil  ? 

44.  What  effect  does  water  have  on  ease  of  puddling? 

45.  Why  does  plowing  tend  to  puddle  a  wet  soil  ? 

46.  What  agencies  destroy  a  puddled  condition? 

47.  Why  is  fall  plowing  of  heavy  soils  beneficial  ? 

48.  What  advantages  do  silt  soils  possess  over  clays? 

49.  What  about  shrinkage  and  granulation  of  silt  soils? 

50.  Why  does  sand  possess  little  tenacity  ? 

51.  What  effect  does  this  have? 

52.  What  is  "  firing"  of  corn  and  what  is  the  cause? 

53.  What  value  has  gravel  in  soils? 

54.  What  value  have  stones  in  soils? 

55.  Define  tenacity. 

56.  Of  what  value  are  colloids  in  soils? 

57.  What  property  causes  black  clay  loam  to  ''  roll  "  upon  wagon  wheels? 


MINERAL  CONSTITUENTS  141 

REFERENCES 

1  Briggs,  L.  J.,  Martin,  F.  O.,  and  Pearce,  J.  R.,  Bulletin  24,  Bureau  of  Soils, 
U.S.D.A.,  The  Centrifugal  Method  of  Soil  Analysis,  1904,  p.  33. 

'Wilev,  H.  VV.,  Principles  and  Practice  of  Agricultural  Analysis,  1906,  p. 
231. 

*  Op.  Cit.,  p.  246. 

4  Bulletin  24,  Bureau  of  Soils,  1904,  p.  12. 

•Yoder,  P.  A.,  Bulletin  89,  Utah  Station,  The  New  Centrifugal  Soil 
Elutriator,  1904. 

•King,  F.  H.,  Physics  of  Agriculture,  1907,  p.  121. 

TZt.  f.  phys.  Chem.,  Leipsic,  9.  88   (1802). 

1  Unpublished  data,  Soil  Physics  Division,  University  of  Illinois. 

General  References. — Fletcher.  C.  C.,  and  Bryan,  H.,  Bulletin  84, 
Bureau  of  Soils,  U.S.U.A.,  Modification  of  the  Method  of  Mechanical 
Analysis,  1912.  Rohland,  Paul.  The  Colloidal  and  Crystalloidal  States  of 
Matter,  1914,  I).  Von  Nostrand  Co.,  New  York.  Hatschek,  Emil,  An  Intro- 
duction to  the  Physics  and  Chemistry  of  Colloids,  1913,  J.  &  A.  Churchill, 
Ix>ndon.  Oatwald,  translated  by  Fischer,  Handbook  of  Colloid-Chemistry, 
1915,  P.  Blakiston'a  Sons  &  Co.,  Philadelphia. 


CHAPTER   XI 

ORGANIC  CONSTITUENTS  OF  SOILS 

BY  far  the  most  valuable  constituent  of  soils  is  the  organic  mate- 
rial derived  from -the  plants  and  animals  that  have  lived  in  and 
on  the  soil.  The  term  organic  matter  will  he  used  to  include  all 
material  from  organisms,  to  distinguish  it  from  the  term  humus  of 
more  restricted  use.  Humus  refers,  in  its  restricted  meaning,  only 
to  that  portion  of  organic  matter  that  is  soluble  in  dilute  alkali. 

Kinds  of  Organic  Matter. — Organic  matter  exists  in  the  soil  in 
every  stage  of  decay,  from  that  whose  cellular  structure  is  still  visi- 
ble, to  that  very  similar  to  coal.  It  may  be  divided  into  (a)  active 
or  fresh,  which  decomposes  readily;  (b)  the  inert,  which  is 'usually 
old  and  decomposes  too  slowly  for  the  use  of  crops;  and  (c)  the 
coal-like  material  that  oxidizes  with  extreme  slowness,  if  at  all,  and 
whose  chief  use  is  to  impart  a  dark  color  to  the  soil  (Figs.  74  and 
To).  The  active  is  the  most  important  and  is  that  form  which  is 
ordinarily  supplied  to  the  soil  as  manure  and  legumes.  Under  long- 
continued,  injudicious  systems  of  cropping  the  active  organic  matter 
is  largely  removed  and  the  result  is  exhausted,  "  run-down  "  or 
"worn-out"  land.  To  maintain  the  productiveness  the  organic 
matter  must  be  supplied  in  considerable  quantities  and  of  a  form 
that  will  decay  readily.  It  is  equally  essential  to  supply  organic 
matter  in  a  more  stable  or  less  readily  decaying  form,  as  straw, 
corn  stalks  or  other  non-leguminous  material,  since  these  benefit  the 
soil  physically  for  a  longer  time  than  legumes. 

Amount  of  Organic  Matter  in  Soils. — The  organic-matter 
content  of  soils  varies  quite  widely  in  the  same  locality.  Even  in 
soils  from  which  it  has  not  been  removed  by  erosion  a  distance  of 
a  few  rods  may  make  a  great  difference  in  the  amount.  Soils  con- 
tain from  a  small  fraction  of  a  per  cent  to  90  per  cent.  Swamp 
lands  generally  contain  most,  while  sand  soils  contain  least. 

How  much  organic  matter  a  soil  should  contain  is  a  question 
often  asked  and  one  very  difficult  to  answer.  A  soil  may  contain 
five  per  cent  of  organic  matter  and  be  less  productive  than  one  with 
only  two  per  cent.  Much  depends  upon  its  activity  or  rapidity  of  de- 
composition. The  chances  for  large  yields  are  decidedly  in  favor  of 
the  soil  with  a  large  organic  content.  A  soil  with  a  few  tons  of  fresh 
142 


ORGANIC  CONSTITUENTS  OF  SOILS  143 

or  quickly  decaying  organic  matter,  such  as  clover  or  manure,  may 
give  better  results  than  a  soil  full  of  old,  slowly  decomposing  organic 
matter  unless  the  conditions  are  most  favorable.  There  should  be 
sullicient  organic  matter  to  keep  the  soil  in  good  physical  condition 
and  also  furnish  nitrogen  for  maximum  crops.  The  organic  con- 
tent depends  upon  several  factors,  as  follows: 

(a)  Moisture  exerts  a  double  influence  in  aiding  the  accumula- 
tion of  organic  matter  in  soils.  In  the  first  place,  it  is  favorable  to 
the  growth  of  plants.  It  makes  very  little  difference  how  little  or 
how  much  moisture  is  present  in  the  soil,  some  plants  have  adapted 
themselves  to  growing  under  those  conditions.  Even  where  water 
stands  nearly  all  the  year,  cat-tails,  flags,  sedges,  and  some  grasses 

Fio.  74.  FIQ.  75. 


Fio.  74. — Fragments  of  plants  found  in  soils.      (Bulletin  !>0,  Bureau  of  Soils.) 
Fio.   75.— Fragments  of  insects  found  in  soils. 

grow  luxuriantly.  In  the  second  place,  the  presence  of  excessive 
moisture  tends  to  preserve  the  plants,  which  ultimately  form  soil 
themselves  or  become  mixed  with  the  mineral  matter  and  aid  in 
forming  soil,  such  as  peats,  peaty  loams,  and  mucks.  M ven  soil  with 
an  ordinary  amount  of  moisture  prevents  complete  oxidation  of  the 
roots  and  other  fresh  vegetable  material  that  becomes  incorporated 
with  it.  Soils  containing  small  amounts  of  water,  such  as  sands 
provide  very  favorable  conditions  for  oxidation,  and  hence  the 
organic-matter  content  of  such  soil  is  low. 

Overflow  land  generally  contains  more  than  the  adjacent  upland 
because  of  the  greater  growth  due  to  a  richer  soil,  the  better  facilities 
for  its  preservation  because  of  greater  moisture  content,  and  the 
deposition  of  some  organic  matter  along  with  the  sediment  during 
periods  of  overflow.  This  deposit  may  cover  leaves  and  grasses,  thus 
preserving  them  from  complete  decay. 


144 


SOIL  PHYSICS  AND  MANAGEMENT 


Arid  soils  are  naturally  low  in  organic  matter  because  the  moist- 
ure is  not  sufficient  to  produce  a  large  growth  of  vegetation. 

(b)  Vegetation. — The  upland  timber  soils  contain  much  less 
organic  matter  than  the  adjacent  prairies.  It  is  safe  to  assume  that 
the  prairies  were  much  more  extensive  formerly  than  now.  Newly 
formed  lands  were  originally  treeless  and  covered  by  smaller  plants, 
but  more  especially  grasses.  This  was  particularly  true  in  the  glaci- 
ated area.  The  prairies  were  covered  with  grasses  whose  network 
of  roots  extended  to  a  depth  of  8  to  20  inches  or  more.  A  sample  of 
virgin  blue  stem  prairie  sod  on  brown  silt  loam  contained  roots  at 
the  rate  of  IS1/^  tons  per  acre  to  the  depth  of  6%  inches.  Part  of 
these  roots  died  each  year,  and  the  partially  decayed  material 
accumulated  in  the  soil,  forming  the  black  prairie  soils  of  the  corn 
belt.  In  Illinois  the  analyses  of  302  samples  show  the  surface  soil  to 
a  depth  of  6%  inches  to  contain  4.53  per  cent,  or  about  45  tons  of 
organic  matter  per  acre.  This  includes  the  rolling  and  flat  prairie 
soils,  but  not  the  swamps.  The  subsurface,  6%  to  20  inches  in  depth, 
showed  an  organic-matter  content  of  2.8  per  cent. 

That  this  is  probably  true  as  to  the  origin  of  the  black  earth  soil 
or  chernozem  of  Russia  is  well  shown  by  the  following  table  which 
gives  the  relative  amount  of  roots  and  percentage  of  humus  in  six- 
inch  depths: 

Roots  and  Humus  in  Three  Chernozem  Soils  at  Different  Depths.     The  Roots 
in  the  Surface  Six  Inches  is  Taken  as  100  Per  cent 


l 

2 

c 

Roots 

Humus 

Roots 

Humus 

Roots 

Humus 

0-  6  inches  .    . 

100 

5.42 

100 

8.11 

100 

9.64 

6-12  inches  .    . 

89.1 

4.83 

63.9 

5.19 

80.3 

7.77 

12-18  inches  .    . 

66.9 

3.62 

48.3 

3.92 

70.0 

6.71 

18-24  inches  .    . 

47.3 

2.56 

35.0 

2.84 

58.4 

5.81 

24-30  inches  .    . 

47.3 

2.50 

26.0 

2.11 

38.2 

3.57 

30-36  inches  .    . 

34.6 

1.88 

18.1 

1.47 

33.0 

3.18 

36-42  inches.    . 

23.9 

1.29 

6.3 

.51 

16.2 

1.56 

42^48  inches  .    . 

14.4 

.78 

.70 



48-54  inches 

67 

.36 

These  determinations  are  rather  typical  for  semi-arid  or  rather 
sub-humid  prairie  soils  where  there  is  a  greater  tendency  for  the 
roots  to  penetrate  deeply.  A  similar  condition  exists  in  humid  soils, 
with  this  difference,  that  the  great  mass  of  roots  is  nearer  the  surface. 

The  invasion  of  the  prairies  bv  forests  has  been  goiner  on  very 
slowly.  The  first  trees  to  spread  over  the  prairies  were  wild  cherry, 


ORGANIC  CONSTITUENTS  OF  SOILS  145 

black  walnut,  hackberry,  elm,  ash,  and  bur-oak.  The  shade  of  the 
trees  and  the  undergrowth  that  slowly  crept  in  killed  the  grasses, 
and  the  plants  that  replaced  them  supplied  very  little  organic  mat- 
ter to  the  soil.  The  leaves  and  twigs  accumulated  upon  the  surface 
and  decayed  completely  or  were  burned  by  forest  fires.  The  organic 
matter  that  had  accumulated  was  slowly  being  removed  by  oxidation 
of  nitrification,  with  the  result  that  the  soils  were  gradually  changed 
until  a  light-colored  soil  resulted.  When  this  change  had  taken 
place  the  trees  mentioned  above  were  gradually  replaced  by  white 
oak,  hickory,  and  others  adapted  to  light-colored  soils  or  soils  low  in 
organic  matter.  Several  generations  of  trees  were  required  to  effect 
this  change.  So  great  was  the  reduction  of  organic  matter  that  the 
timber  soils  contain  less  than  half  as  much  as  the  prairie.  The  anal- 
yses of  1(54  samples  of  timber  soil  show  1.93  per  cent  in  the  surface 
and  0.77  per  cent  in  the  subsurface. 

(c)  Limestone. — Soils  rich  in  limestone  are  usually  well  sup- 
plied with  organic  matter,  due  to  the  fact  that  limestone  encourages 
a  larger  growth  of  vegetation,  especially  of  legumes,  and  is  very 
effective  in  retaining  humus  in  the  soil  against  leaching. 

(d)  Latitude  and  Altitude. — As  a  general  rule  soils  of  north- 
ern  latitudes  have  more  organic  matter  than  those  of  southern. 
While  the  conditions  for  a  luxuriant  growth  of  vegetation  are  not  so 
favorable  in  the  north,  yet  the  conditions  for  its  preservation  are  so 
much  better  that  the  result  is  a  larger  organic  content.    This  is  well 
shown  in  Illinois.    The  deposit  of  loess  in  the  State  along  the  Mis- 
sissippi liiver  is  the  same  throughout  the  length  of  the  State.    The 
analyses  of  eight  samples  of  deep  loess  from  the  south  end  of  the 
State  show  1.11  per  cent  of  organic  matter,  while  four  samples  from 
the  north  end  show  3.K(!  per  cent.    Eighteen  samples  of  timber  soil 
from  the  south  end  of  the  State  show  1.5  per  cent  of  organic  matter 
in  the  surface  and  0.58  |HT  cent  in  the  subsurface,  while  the  same 
general  character  of  soils  in  the  north  shows  2.4  and  0.0(5  per  cent 
respectively.     The  same  is  true  of  the  prairie  soils.     The  brown 
prairie  soils  from  the  lattiudo  of  the  southern  part  of  the  early  Wis- 
consin glaciation  show  4.5  per  cent,  while  the  samo  type  150  miles 
to  the  north  contains  (5.1  per  cent. 

Changes  of  Organic  Matter. — When  vegetable  matter  becomes 
mixed  with  soil  it  undergoes  a  physical  change  produced  by  bacterial 
action  in  which  the  plant  tissues  are  destroyed,  and  it  becomes  A 
black  or  dark  brown  homogeneous  mass.  At  the  same  time  a  chem- 
ical change  takes  place.  The  process  at  first  is  quite  rapid,  but  later 
10 


146 


SOIL  PHYSICS  AND  MANAGEMENT 


becomes  very  slow,  and  still  later  ceases  almost  entirely.  The  supply 
of  oxygen  is  somewhat  low  in  the  soil  and  the  conditions  are  not 
favorable  for  complete  oxidation  of  the  vegetable  matter.  The 
partial  oxidation  produces  organic  matter  of  varied  composition. 
In  this  change  the  hydrogen  and  oxygen  content  of  the  vegetable 
matter  becomes  less,  while  the  proportion  of  carbon  and  nitrogen 
increases.  The  organic  matter  of  the  soil  under  different  conditions 
may  contain  from  three  to  twenty  times  as  much  nitrogen  as  the 
original  material.  This  change  may  be  carried  so  far  that  ultimately 
carbonized  material  may  be  produced  that  is  similar  to  coal  or  char- 

FIG.  76.  FIG.  77. 

~T 


FIG.  76. — Specimens  of  charcoal  and  charcoal-like  material  found  in  soils. 
FIG.  77. — Specimens  of  coal  found  in  soils.     (Bulletin  90,  Bureau  of  Soils.) 

coal1  (Figs.  76  and  77).  This  does  not  undergo  further  change. 
The  humus  accumulates  more  rapidly  in  very  moist  soils  than  in 
comparatively  dry  ones. 

The  following  table  from  Hilgard  shows  the  changes  in  the  for- 
mation of  coal,  probably  somewhat  similar  to  those  changes  of 
organic  matter  in  soils : 

Progress  of  H unification,  and  Formation  of  Coal  *  (Moisture  and  Ash  Omitted 

From  Calculations) 


Cellu- 
lose 

Humin 
and  humic 
acid 

Peat 

Coals 

Brown 

Black 

Lignite 
brown 
coal 
(Bovey) 

Scotch 
splint 
bitu- 
minous 

Penn- 
syl- 
vania 
anthra- 
cite 

Sur- 
face 
(Ulmin) 

40 
inches 

80 
inches 

Carbon  

44.44 
6.17 
49.38 

49.4-59.7 
2.5-  4.5 
35.8-47.3 
.3-18.7 

57.80 

5.40 
36.00 
.80 

62.00 
5.20 
30.70 
2.10 

64.10 
5.00 
26.80 
4.10 

69.50 
5.90 
24.00 
.60 

84.20 
5.80 
8.80 
1.20 

94.80 
2.60 

J2.60 

Hydrogen  

O  xv  Ken 

Nitrogen  

ORGANIC  CONSTITUENTS  OF  SOILS 


147 


While  this  table  does  not  represent  exactly  the  changes  that  take 
place  in  the  soil  under  all  conditions,  yet  Schriiier  and  Brown 
have  shown  that  many  particles  of  coal  and  charcoal-like  material 
exist  in  the  soil,  indicating  that  this  process  probably  occurs  in  soils. 
Some  of  this  may  be  the  result  of  fires. 

Nitrogen  Content  of  Humus. — Moisture  plays  a  very  impor- 
tant part  in  determining  the  composition  of  organic  matter  of  soils, 
indicating  that  the  process  of  humification  is  quite  varied  under 
different  conditions.  This  difference  is  well  shown  in  the  nitrogen 
content  of  humus  from  arid  and  humid  regions.  Hilgard  has  shown 
that  soils  of  California  vary  in  humus  content  with  the  rainfall,  but 
their  nitrogen  appears  to  be  independent  of  humidity. 

Humus  and  Nitrogen  Content  of  Humid  and  Arid  Soils  of  California  3 


Humus 

Nitrogen  in 
humus 

Nitrogen  in 
soil 

Arid  soils,  California  

percent 
.91 

percent 

15.23 

per  cent 

.135 

Sub-irrigated  arid,  California  

1.06 

8.38 

.099 

Humid  soils,  California  

2.45 

5.29 

.135 

Later  investigations  seem  to  indicate  that  the  nitrogen  content 
of  the  humus  in  arid  soils  is  not  as  high  as  the  above  figures  show. 
The  organic  matter  of  humid  regions  contains  a  somewhat  vari- 
able amount  of  nitrogen.  One  hundred  and  twenty-six  surface  sam- 
ples of  prairie  soils  contained  5.1  per  cent  of  organic  matter,  the 
nitrogen  of  which  was  approximately  4.88  per  cent.  The  average 
organic-matter  content  of  M  surface  samples  of  timber  soils  wa^  l.!>3 
per  cent,  which  contained  5.09  per  cent  of  nitrogen.  By  multiplying 
the  nitrogen  content  of  a  humid  soil  by  20  a  fair  approximation 
of  the  amount  of  organic  matter  may  be  obtained. 

The  character  of  soil  humus  will  also  depend  upon  the  character 
of  the  material  from  which  it  is  derived.  Snyder,  of  Minnesota,  has 
determined  the  amount  of  nitrogen  in  humus  from  different  sources. 
The  Amount  of  Nitrogen  in  Humus  from  Different  Materials  4 


Humus  from  meat  scraps  

10.96  per  cent  nitrogen 

Humus  from  green  clover  

8.94  per  cent  nitrogen 

Humus  from  cow  manure  

6.16  per  cent  nitrogen 

Humus  from  oat  straw  

2.50  per  cent  nitrogen 

Humus  from  sawdust.           .  .    . 

32  per  cent  nitrogen 

Distribution  of  Organic  Matter  in  the  Soil  Strata. — The  con- 
tent of  organic  matter  diminishes  with  depth  in  all  normal  soils  so 
that  at  from  three  to  six  feet  the  amount  becomes  very  low.  In  arid 


148 


SOIL  PHYSICS  AND  MANAGEMENT 


soils  the  content  runs  more  uniform  and  to  greater  depth,  due  to 
deeper  root  development.  In  swamp  soils  there  is  frequently  a 
great  accumulation  in  the  surface  and  upper  subsurface,  with  rather 
a  sudden  decrease  at  a  distinct  line.  Timber  soils  show  a  greater 
decrease  in  the  subsurface  than  prairie  soils.  The  organic  matter 
is  usually  deeper  in  alluvial  soils  than  in  others.  The  distribution 
depends  to  a  large  extent  upon  the  depth  of  root  development,  the 
effect  of  burrowing  animals,  the  accumulations  that  are  taking  place 
as  in  bottom  and  swamp  lands  and  the  cracks  produced  by  shrink- 
age, which  is  especially  characteristic  of  clay  and  clay  loam  soils. 

Organic  Matter  in  Soil  Strata,  * 


Soil  types 

No.  of 
samples 

Surface 
0-62/3 
inches 

Subsurface 
6  2/3-20 
inches 

Subsoil 
20-40 
inches 

Brown  silt  loam  

122 

per  cent 

5.30 

per  cent 

3.10 

per  cent 

0.91 

Black  clfl/y  loam      

29 

7.03 

3.58 

1.02 

Yellow-gray  silt  loam              

51 

2.33 

0.89 

0.57 

Yellow  silt  loam  

35 

1.76 

0.69 

0.48 

Gray  silt  loam  on  tight  clay  

18 

2.40 

1.31 

0.70 

Value  of  Organic  Matter  to  Soils. — It  is  next  to  impossible 
to  assign  a  definite  money  value  to  organic  matter  as  in  the 
case  of  nitrogen,  phosphorus,  and  potassium.  The  difficulty  arises 
from  the  fact  that  vhen  incorporated  with  the  soil  it  has  sev- 
eral different  effects,  physical,  chemical,  and  biological,  any  one  of 
which  is  of  sufficient  importance  to  justify  its  use.  The  value  of 
organic  matter  must  in  the  end  be  determined  from  the  value  of  the 
increase  in  crops  produced.  This  has  been  worked  out  for  manure 
and  is  being  determined  for  other  forms  of  organic  matter,  such  as 
crop  residues  and  legumes.  The  things  for  which  it  is  of  value  are 
as  follows : 

1 .  Granulation  is  one  of  the  most  important  properties  of  heavy 
and  medium  soils.  This  gives  permeability  for  both  air  and  water, 
and  very  desirable  working  qualities  that  heavy,  non-granular  soils 
do  not  possess.  In  fact,  some  of  the  most  intractable  soils  are  clays 
that  are  quite  low  in  organic  matter.  The  granular  structure  lessens 
the  tenacity.  This  latter  is  especially  noticeable  in  heavy  soils. 
There  is  no  one  constituent  so  beneficial  to  such  a  large  class  of  soils 
as  organic  matter.  Its  removal  from  a  soil  destroys  its  power  to 
granulate  almost  entirely.  When  the  humus  is  taken  from  brown  silt 


ORGANIC  CONSTITUENTS  OF  SOILS 


149 


loam  and  black  clay  loam  by  leaching  with  dilute  ammonia,  the 
power  to  granulate  is  lost. 

Figure  78  shows  the  effect  of  removal  of  humus  upon  the  granu- 
lation of  black  clay  loam  and  drab  clay.  The  silt  loams  granulated 
very  little  even  with  organic  matter.  Each  soil  has  been  wet  and 
dried  several  times.  Cropping  with  the  continued  removal  of 
organic  matter  will  ultimately  bring  about  a  condition  of  poor 
granulation  and  consequently  poor  tilth. 

3.  Retaining  Moisture. — There  is  no  better  method  of  increas- 
ing the  moisture  holding  capacity  of  soils  than  by  adding  organic 


Fio.  78. — The  effect  of  the  removal  of  humus  and  of  wetting  and  drying  upon  granula- 
tion. Drab  clay  is  the  only  one  that  shows  any  tendency  to  granulate  when  humus  is  re- 
moved. (University  of  Illinois.) 

matter.  It  acts  as  a  sponge  itself,  and  when  mixed  with  the  mineral 
part  of  the  soil  gives  higher  porosity  and  consequently  reater  water 
capacity.  Jt  retards  capillary  movement  in  soils,  as  \\oll  as  aids  in 
the  production  of  a  better  mulch,  both  of  which  help  in  retaining 
moisture  by  reducing  evaporation.  Sand  permits  of  rapid  percola- 
tion with  comparatively  small  amounts  of  water  retained.  I  f  organic 
matter  is  added  to  sand,  the  retentive  power  of  sand  will  be  greatly 
increased.  This  table  shows  the  effect. 

Effect  of  Organic  Matter  on  Retention  of  Moisture  in  Sand  8 


Soil  material 

Grams  of 
.vater  retained 
by  1(K)  grams 

Increase, 
per  rent 

Coarse  sand  

13.3 

Coarse  sand  with    5  per  cent  peat               

18.6 

40.0 

Coarse  sand  with  10  per  cent  peat 

24.7 

85.7 

Coarse  sand  with  20  per  cent  peat  

40.0 

200.7 

Peat  

184.0 

1283.4 

150  SOIL  PHYSICS  AND  MANAGEMENT 

The  movement  of  capillary  moisture  is  principally  along  the 
surfaces  of  mineral  soil  particles  that  are  in  contact,  and  the  more 
points  of  contact  the  larger  the  amount  and  the  greater  the  rapidity 
of  movement.  Organic  matter  introduces  many  very  irregular  par- 
ticles which  diminish  the  number  in  contact.  As  a  result  capillary 
movement  is  slow  in  soils  rich  in  organic  matter. 

3.  Puddling. — The  particles  of  soils  low  in  organic  matter  are 
not  cemented  together  into  crumbs  and  hence  are  free  to  move. 
When  these  dry  soils  become  wet  there  is  a  rearrangement  of  the 
particles,  due  to  the  drawing  force  of  the  surface  film,  by  which  they 
are  brought  closer  together,  and  the  pore  space  is  so  diminished  that 
water  cannot  penetrate  the  wet  stratum  very  rapidly.  This  is  spoken 
of  as  "running  together,"  but  is  really  one  form  of  puddling.    The 
change  is  produced  by  the  tension  of  the  film  of  water  drawing  the 
particles  together.    This  action  may  be  seen  where  drops  of  water 
fall  in  dust  during  a  shower. 

Soils  low  in  organic  matter  are  easily  puddled  if  worked  when 
wet,  and  a  longer  time  is  required  for  the  natural  agencies  to  correct 
this  condition  than  if  the  soil  is  well  provided  with  organic  matter. 
Since  granules  are  destroyed  by  puddling  a  correction  of  this  con- 
dition is  produced  when  by  any  means  granulation  is  restored. 

4.  Prevents  Loss  by  Erosion. — Erosion  causes  very  serious 
loss  on  many  soils.     A  vast  amount  of  the  richest  soil  material  is 
removed  annually  from  the  rolling  land  by  the  excess  of  rainfall 
that  runs  off  as  surface  drainage.    The  more  the  run-off  the  greater 
the  amount  of  washing.    It  is  practically  impossible  to  prevent  this 
entirely.      The    loss    may   be    diminished   by   methods   given    in 
Chapter  xxvii. 

5.  Increases  Temperature. — Organic  matter  imparts  a  darker 
color  to  the  soil,  thus  increasing  the  absorption  of  heat,  and  raising 
the  temperature,  and,  as  a  general  rule  for  well-drained  soils,  the 
darker  the  soil  the  higher  the  temperature.    Light-colored  soils  are 
cold,  while  dark  ones  are  warm.     This  difference  in  color  may 
increase  the  temperature  from  four  to  ten  degrees  F.  at  a  depth  of 
four  inches  during  a  clear  day  and  give  the  crop  on  the  dark  soil  a 
distinct  advantage. 

0.  Biological  Effects. — Biological  and  consequently  chemical 
action  is  increased  by  organic  matter,  not  only  because  it  provides 
a  food  supply  for  the  organisms,  but  also  because  it  brings  about 
physical  conditions  favorable  to  the  action  of  bacteria  which  produce 
chemical  action. 


ORGANIC  CONSTITUENTS  OF  SOILS  151 

7.  Furnishes  Nitrogen  to  Crops. — The  only  source  of  nitrogen 
for  our  non-leguminous. crops  is  organic  matter.     Nitrogen  starva- 
tion goes' hand  in  hand  with  low  organic  content  in  soils.    This  is 
evidenced  by  the  yellowish-green  color  of  corn,  oats,  or  wheat  on 
eroded  land  deficient  in  organic  matter  in  contrast  to  the  dark  green 
color  where  this  constituent  is  abundant.    It  supplies  nitrogen,  the 
most  expensive  food  element  used  by  plants,  one  that  we  cannot 
afford  to  buy  for  ordinary  farm  crops.    A  100-bushel  crop  of  corn 
per  acre  requires  150  pounds  of  nitrogen,  the  commercial  value  of 
which  at  15  cents  per  pound  is  about  $22.50.     Other  crops  require 
somewhat  similar  amounts.     Legumes  are  independent  of  organic 
matter,  as  they  obtain  their  nitrogen  from  the  air. 

8.  Binds  Soil  Particles  Together. — On  sandy  soils  well-decom- 
posed organic  matter  binds  the  sand  grains  together  and  reduces 
movement  by  wind.    It  also  increases  the  water-holding  capacity,  as 
seen  before. 

Losses  of  Organic  Matter. — The  amount  of  organic  matter 
in  the  surface  stratum  of  the  ordinary  upland  soils  varies  from 
15  to  60  tons  per  acre.  This  has  required  thousands  of  years 
for  its  accumulation,  but  through  the  systems  of  cropping  generally 
practiced  it  is  being  removed  from  the  soils  much  more  rapidly 
than  it  ever  accumulated. 

(a)  By  Cropping. — The  amount  of  organic  matter  removed 
annually  from  a  soil  well  supplied  with  it  in  reasonably  active  form, 
such  as  brown  silt  loam,  is  not  far  from  three-fourths  to  one  ton  per 
acre.  A  large  portion  of  this  is  used  indirectly  by  the  crop,  while  the 
remainder  is  lost  by  the  natural  processes  described  below.    In  com- 
paring a  virgin  prairie  soil  with  the  same  soil  after  cropping  for 
sixty  years,  it  was  found  that  the  organic-matter  content  of  the  soil 
has  been  reduced  approximately  fifty  tons  per  acre.     Of  course,  in 
soils  with  a  smaller  amount  of  organic  matter  the  total  removed  is 
necessarily  less.    The  amount  removed  depends  to  some  extent  upon 
the  crop  grown.    The  inter-tilled  crops  use  more  nitrogen,  and  more 
organic  matter  would  be  decomposed  to  produce  it  than  non-tilled 
crops.     It  must  be  remembered  that  loss  of  nitrates  either  by  crop- 
ping or  leaching  means  loss  of  organic  matter  from  the  soil. 

(b)  By  Erosion. — Organic  matter  may  be  removed  from  the 
soil  by  erosion.    Very  few  regions  are  so  flat  or  have  the  soil  so  well 
protected  that  there  is  not  more  or  less  erosion  taking  place,  and  in 
the  more  rolling  areas  this  becomes   a   very  active   agent   in   the 
removal  of  the  organic  matter  along  with  the  soil.     In  this  way  in 


152  SOIL  PHYSICS  AND  MANAGEMENT 

certain  regions  almost  all  of  the  surface  soil  and  its  organic  matter 
have  been  removed,  and  yellow  "  clay  points  "  are  quite  common. 
These  are  nothing  more  than  the  outcropping  of  a  stratum,  either 
of  subsurface  or  subsoil,  which  contains  little  or  no  organic  matter. 
Even  on  brown  silt  loam  areas  much  loss  of  organic  matter  takes 
place  through  erosion,  and  this  becomes  more  serious  the  longer 
cropping*continues. 

(c)  By  Leaching. — In  the  partial  decomposition  of  vegetable 
matter  soluble  organic  acids  are  formed.    These  may  be  removed  in 
part  by  the  water  which  percolates  through  the  soil  during  heavy 
rains.    This  is  especially  true  of  acid  soils.    It  is  not  uncommon  to 
see  the  drainage  water  of  peat  bogs  of  a  brownish  color,  due  to  the 
dissolved  organic  matter.  The  presence  of  small  amounts  of  certain 
alkalies,  as  ammonia  and  sodium  carbonate,  increases  the  solvent 
power  of  water  for  humus. 

(d)  By  Fires. — Fires  of  even  moderate  intensity  destroy  large 
amounts  of  organic  matter  from  the  immediate  surface,  and  even  in 
the  burning  of  straw,  stubble,  or  corn  -stalks  considerable  organic 
matter  is  lost  from  the  soil.    Snyder 7  gives  the  following :    "  The 
soil  from  Hinckley,  Minnesota,  before  the  great  forest  fire  of  1893 
showed  1.69  per  cent  humus  and  0.12  per  cent  nitrogen.  After  the 
fire  there  were  present  0.41  per  cent  humus  and  0.03  per  cent  nitro- 
gen.   The  forest  fire  had  caused  a  loss  of  2500  pounds  of  nitrogen 
per  acre,  or  thirteen  tons  of  organic  matter."  Much  organic  matter 
that  should  be  plowed  back  into  the  soil  is  burned. 

(e)  By  Oxidation  or  Nitrification. — The  process  of  oxidation 
is  carried  on  through  the  influence  of  bacteria  which  are  always 
present  in  fertile  soils.     Under  favorable  conditions  of  moisture, 
temperature,  and  aeration  these  organisms  are  very  active  agents  in 
destroying  organic  matter.    They  are  especially  active  in  cultivated 
and  well-aerated  soils,  and  while  their  work  means  destruction  to 
organic  matter,  they  are  at  the  same  time  performing  a  function 
absolutely  necessary  for  the  growth  of  plants.     In  the  destruction 
of  organic  matter  they  are  producing  plant  food  essential  for  crops. 
In  the  growing  of  crops,  one  and  one-half  pounds  of  nitrogen  are 
required  for  a  bushel  of  corn,  one  for  oats,  and  two  for  a  bushel  of 
wheat,  and  this  must  be  obtained  from  organic  matter  through  the 
agency  of  these  bacteria.    The  greatest  loss  occurs  when  no  crop  is 
growing,  and  these  soluble  plant  foods  are  lost  by  leaching,  although 
some  loss  of  nitrates  is  nroincr  on  whenever  drainage  takes  place. 

(f)  By  Use  of  Quicklime.  —  A  very  serious  objection  to 


ORGANIC  CONSTITUENTS  OF  SOILS 


153 


burned  limestone  or  quicklime  is  that  it  tends  to  destroy  the  organic 
matter  of  the  soil,  and  most  soils  that  need  lime  have  too  little 
organic  matter  to  begin  with.  At  the  Pennsylvania  Station  the  plots 
having  burnt  lime  applied  for  25  years  showed  less  nitrogen  by 
375  pounds  than  the  limestone  plot.  This  difference  is  equal  to 
37.5  tons  of  barnyard  manure  per  acre.  At  the  Virginia  Station  it 
has  been  determined  that  the  applications  of  quicklime  have  reduced 
the  amount  of  nitrogen  and  organic  matter  when  compared  with 
plots  treated  the  same  except  that  quicklime  was  omitted. 

(g)  By  Fallowing. — Fallowing  is  leaving  the  land  without  a 
crop  for  a  season  during  which  the  soil  is  cultivated.  This  has  been 
a  very  common  agricultural  practice  in  European  countries,  but 
more  especially  in  England.  The  objects  of  the  fallow  were  to 
destroy  weeds,  to  develop  an  abundance  of  nitrates  for  the  succeeding 
crop,  to  increase  the  moisture  content  of  the  soil,  and  to  produce 
good  tilth  in  heavy  soils.  While  all  of  the  objects  were  accomplished, 
yet  in  regions  where  heavy  fall,  winter,  or  spring  rains  occur  much 
of  the  soluble  plant  food  which  was  produced  at  the  expense  of 
organic  matter  was  leached  out  of  the  soil  and  lost.  King  found 
that  in  the  spring  of  1900  land  fallowed  the  previous  season  con- 
tained 245.7  pounds  more  of  nitrates  per  acre  than  the  cropped 
land.  The  following  table  from  Hall  shows  the  effect  of  leaching 
from  fallowed  land  upon  the  wheat  crop : 

Yield  of  Wheat  Grown  When  Percolation  loos  Large  and  Small8 


Percola- 

Bushels per  acre 

tion 
through 
OO-inch 
gauge 

Tile  ran 
days 

Wheat 
after 
wheat 
earh  year 

Wheat 
after 
fallow 

Gain 
due  to 
fallow 

15  years  of  percolation, 

3.99 

4 

30.1 

44.6 

14.5 

below  average 

16  years  of  percolation, 
above  average 

8.92 

13 

27.1           29.3 

2.2 

Loss  due  to  excess  leaching 

3.0            15.3 

Fallowing  should  bo  practiced  only  where  the  rainfall  is  not 
sufficient  to  cause  any  loss  by  leaching,  as  in  sub-humid  and  somi- 
arid  regions. 

Estimation  of  Organic  Matter. — Xo  very  satisfactory  method 
has  been  devised  for  determining  the  organic  matter  of  soils,  since 
it  is  impossible  to  determine  it  directly. 


154 


SOIL  PHYSICS  AND  MANAGEMENT 


(a)  Loss  on  Ignition." — The  ignition  method  is  sometimes 
used,  but  at  the  best  is  only  approximate  for  peats  and  sands 
which  contain  very  little  water  of  hydration.  Five  grains  of  water- 
free  soil  is  heated  to  low  redness  in  a  crucible  till  all  organic  matter 
is  burned  away.  Cool  and  moisten  with  a  few  drops  of  a  saturated 
solution  of  ammonium  carbonate.  Dry  and  heat  to  150°  C.  to 
expel  excess  of  ammonia.  The  loss  in  weight  is  the  organic  matter, 
water  of  hydration,  and  volatile  substances. 

Loss  on  Ignition  Compared  with  Organic  Matter 10 
[Calculated  from  organic  carbon] 


Kind  of  soil 

Between 
100°  and 
ignition 

Between 
120°  and 
ignition 

Between 
150°  and 
ignition 

Organic 
matter  at  58 
per  cent 
carbon 

Old  pasture  

P<T  cent 
9.27 

per  cent 
9.06 

per  cent 
8.50 

per  cent 
6.12 

New  pasture  

7.07 

6.88 

6.55 

4.16 

Arable  soil.    . 

5.95 

5.70 

5.61 

2.44 

Clay  subsoil  .  .  . 

5.82 

5.39 

4.76 

0.65 

The  per  cent  of  loss  on  ignition  is  seen  to  be  much  higher  than 
that  obtained  from  the  actual  amount  of  organic  carbon  determined, 
taking  the  organic  matter  as  containing  58  per  cent  of  carbon  or 
multiplying  the  per  cent  of  carbon  by  1.724. 

(b)  Combustion  in  Oxygen.10 — The  combustion  method  has 
been  used  to  some  extent.    The  soil  is  placed  in  a  porcelain  or  plati- 
num boat  and  ignited  in  a  combustion  tube  partly  filled  with  cupric 
oxide.     The  tube  is  connected  with  a  series  of  bulbs,  those  of  sul- 
phuric acid  for  absorbing  nitrous  fumes  and  water  and  a  weighed 
potash  bulb  for  absorbing  the  carbon  dioxide  formed  during  com- 
bustion.    A  current  of  air  from  which  the  carbon  dioxide  has  been 
removed  by  passing  through  a  potash  bulb  is  drawn  through  the 
tube  by  means  of  an  aspirator.    The  amount  of  carbon  dioxide  pro- 
duced is  then  determined  by  weighing  the  bulb,  and  the  organic 
matter  found  by  multiplying  the  weight  of  carbon  dioxide  by  0.471. 

(c)  The  Chromic  Acid   Method.11 — The  apparatus  consists 
of  a  train  of  flasks  and  bulbs  arranged  as  shown  in  figure  79.     A 
current  of  air  is  drawn  through  the  apparatus  by  an  aspirator  at  /. 
The  carbon  dioxide  is  removed  from  the  air  by  a  solution  of  potas- 
sium hydroxide  in  the  flask  G.    The  combustion  takes  place  in  flask 
F,  into  which  about  ten  grams  of  soil  are  placed,  together  with  five  to 


ORGANIC  CONSTITUENTS  OF  SOILS 


155 


ten  grams  of  pulverized  potassium  bichromate.  //  is  a  condenser. 
A  contains  a  saturated  solution  of  silver  suli'ate  to  absorb  any  hydro- 
chloric acid,  sulphur  trioxide  or  dioxide  that  may  be  generated.  B 
contains  concentrated  sulfuric  acid,  ('  potassium  hydrate,  D  acid 
to  be  weighed  with  C  in  determining  the  weight  of  carbon  dioxide. 
An  acid  guard  bulb  completes  the  train.  The  air  is  allowed  to 
pass  through  the  system  for  about  ten  minutes.  The  soil  and 
potassium  bichromate  are  thoroughly  mixed  in  F  and  concentrated 
sulfuric  acid  (specific  gravity  1.83)  slowly  admitted  through  the 
dropping  funnel  until  the  end  of  the  tube  from  G  is  covered.  If 
no  vigorous  action  takes  place  the  flask  may  then  be  slowly  heated. 
The  heating  should  continue  from  five  to  ten  minutes.  The  bulbs 
C  and  D  are  then  weighed  and  the  amount  of  carbon  dioxide  de- 


Fm.79. — Arrangement  of  apparatus  for  determining  organic  matter  by  chromic  arid  method. 
(Bulletin  24,  Bureau  of  Soils.) 

termined.  The  organic  matter  is  found  by  multiplying  this  by  0.47 1. 
This  method  does  not  seem  to  give  complete  combustion.  A  com- 
parison with  the  dry  combustion  method  shows  that  the  amount  of 
carbon  found  by  oxidation  with  chromic  acid  is  about  ?!>.9  per  cent 
of  that  found  by  the  combustion  method. 

Carton  Found  by  the  Two  Mr'hods  in  Soils  Dried  ni  ICXf  f.1! 


Kind  of  soil 

Combustion 

method 
with  oxygen 

Chromic  arid 
method 

Old  pasture 

per  cent 

3  of) 

prr  rent 

2.81 

New  pasture  .                .... 

2.41 

1  .!« 

Arable  soil     ....                        .          . 

1.42 

1.18 

Subsoil.  . 

0.38 

0.28 

156  SOIL  PHYSICS  AND  MANAGEMENT 

Determination  of  Humus.13 — Ten  grains  of  soil  are  treated 
on  a  filter  successively  with  a  one  per  cent  solution  of  hydro- 
chloric acid  until  the  liine  is  removed,  as  shown  by  testing  a 
few  cubic  centimeters  of  the  filtrate  with  ammonium  oxalate  after 
neutralizing  with  ammonia.  Wash  the  soil  with  distilled  water  to 
remove  the  acid.  The  filter  and  soil  are  placed  in  a  bottle  or  stop- 
pered cylinder  and  a  definite  amount  of  a  four  per  cent  solution  of 
ammonia  is  added.  The  amount  added  should  vary  from  150  to 
500  cubic  centimeters,  depending  upon  the  organic-matter  content 
of  the  soil.  Digest  with  frequent  shaking  for  12  hours  and  allow 
to  stand  for  12  hours.  Filter  the  supernatant  liquid  and  use  an 
aliquot  part  of  the  whole  for  evaporation.  Dry  at  100°  C.,  weigh, 
ignite  and  weigh  again.  The  loss  by  ignition  is  the  humus.  Cal- 
culate the  amount  in  the  entire  -sample. 

QUESTIONS 

1.  Define  organic  matter. 

2.  Distinguish  between  humus  and  organic  matter. 

3.  What  is  the  source  of  most  of  the  organic  matter? 

4.  Why  are  upland  forest  soils  low  in  organic  matter? 

5.  Where  are  chernozem  soils  found? 

6.  What  kinds  of  organic  matter  in  soils ?_ 

7.  What  is  a  "run-down"  farm  usually? 

8.  What  amount  of  organic  matter  should  soils  contain? 

9.  What  effect  does  moisture  have  on  organic-matter  content? 

10.  Are  prairies  increasing  or  decreasing  in  extent? 

11.  How  many  tons  per  acre  of  organic  matter  in  timber  soils  to  a  depth 

of  6%  inches? 

12.  In  the  subsurface? 

13.  Why  are  soils  rich  in  limestone  usually  rich  in  organic  matter? 

14.  Why  do  soils  of  northern  latitudes  have  more  organic  matter? 

15.  Give  the  changes  that  organic  matter  undergoes  in  the  soil. 

16.  Which  elements  increase  and  which  decrease  in  proportion? 

17.  What  is  the  origin  of  the  coal-like  materials  in  soils? 

18.  Compare  the  humus  of  arid  and  humid  regions  in  nitrogen. 

19.  If  the  nitrogen  content  of  a  surface  soil  is  0.287  per  cent,  what  per  cent 

of  organic  matter  does  the  soil  contain  ? 

20.  How  many  tons  per  acre? 

21.  How  is  organic  matter  distributed  in  the  soil  strata? 

22.  How  is  the  money  value  of  organic  matter  to  be  determined?     What 

factors  are  involved? 

23.  Of  what  value  is  granulation? 

24.  What  effect  does  organic  matter   have  on   retention  of  water?     How 

many  tons  of  water  per  acre  will  an  addition  of  5  per  cent  of  peat 
enable  the  surface  to  hold? 

25.  How  does  organic  matter  prevent  puddling? 

26.  How  does  it  aid  in  correcting  it  ? 

27.  What  effect  does  it  have  on  temperature?    How? 
2B.  How  does  it  affect  biological  activity? 


ORGANIC  CONSTITUENTS  OF  SOILS  157 

29.  How  much  nitrogen  is  required  for  a  75-bushel  crop  of  corn  ?     For  a 

60-bushel  crop  of  oats?     For  a  40-bushel  crop  of  wheat? 

30.  What  are  the  evidences  of  nitrogen  starvation? 

31.  Of  what  value  is  organic  matter  in  binding  soil  particles  together? 

32.  What  part  does  erosion  play  in  loss  of  organic  matter? 

33.  What  are  yellow  "  clay  points  "? 

34.  What  part  does  leaching  play  in  loss  of  organic  matter? 

35.  Give  an  example  of  loss  by  fire. 

3(5.  Is  nitrification  beneficial  or  detrimental  to  a  soil? 

37.  What  are  the  objections  to  quicklime? 

38.  What  is  meant  by  fallowing?     Give  the  objects  to  be  accomplished. 

39.  What  effect  does  it  have  on  organic  matter? 

40.  What  was  the  loss  of  organic  matter  due  to  forest  fires? 

41.  Where  may  fallowing  be  practiced  economically?     Why? 

42.  What  objection  to  ignition  for  determining  organic  matter  of  soils? 

43.  Describe  the  dry  combustion  method. 

44.  How  may  the  carbon  of  soils  be  determined? 

45.  Describe  the  method  for  determining  the  humus. 

46.  If  a  soil  contains  1.324  per  cent  of  carbon,  how  many  tons  per  acre  of 

organic  matter  in  the  plowed  soil? 

REFERENCES 

1  Hilgard,  E.  W.,  Soils,  1900,  p.  130,  quoting  Kosticheff. 

'Schreiner,  O.,  and  Brown,  B.  E.,  Bulletin  !)0,  Bureau  of  Soils,  1912,  Occur- 
rence and  Nature  of  Carbonized  Material  in  Soils. 

'  Hilgard,  E.  W.,  Soils,  190(5,  pp.  13(5  and  137. 

*Snyder,  Harry,  Soils  and  Fertilizers,  1908,  p.  105. 

8  Soil  Reports,  Illinois  Station. 

"Unpublished  data  Soil  Physics  Division,  University  of  Illinois. 

7  Snyder,  Harrv,  Soils  and  Fertilizers,  1908,  p.  111. 

•Hall,  A.  I).,  The  Soil,  1903,  p.  109. 

•Wiley,  II.  W.,  Principles  and  Practice  of  Agricultural  Analvsis.  1900,  vol. 
i,*p.  337. 

"Op.  Cit,  p.  352. 

11  Briggs,  I,.  J.,  Martin,  F.  O.,  and  Pearce,  J.  R.,  Bulletin  24,  Bureau  of 
Soils,  1904,  p.  34. 

11  Wiley,  H.  W.,  as  above,  p.  353. 

11  Bulletin  40,  Bureau  of  Chemistry,  U.  S.  I).  A.,  p.  70. 

General  Reference. — Alway,  F.  J.,  and  Bishop,  E.  S.,  Jour,  of  Agr. 
Research,  vol.  v,  No.  20,  1916. 


CHAPTEB   XII 

MAINTAINING   AND    INCREASING   THE    ORGANIC- 
MATTER  CONTENT  OF  SOILS 

THE  maintaining  of  the  organic  matter  in  soils  is  the  most  dif- 
ficult problem  on  the  average  farm.  It,  with  the  nitrogen  it  con- 
tains, is  the  limiting  factor  on  most  of  the  farms  of  the  southern 
and  eastern  states  and  is  fast  becoming  of  primary  importance  on 
corn  and  wheat  belt  farms  of  the  middle  west. 

To  maintain  the  organic  matter  requires  something  else  than 
money.  It  is  not  to  be  had  for  any  price,  because  there  is  no 
adequate  supply.  It  must  be  grown  on  the  farm  and  put  back 
largely  as  residues  which  are  of  low  value  for  any  other  purpose 
or  as  manure  or  both.  To  maintain  this  constituent  requires  very 
careful  planning  of  rotations  and  the  proper  handling  of  the  crops 
grown.  A  few  farmers  may  buy  organic  matter  as  grain  or  hay 
from  their  neighbors,  but  this  is  a  very  short-sighted  policy  for 
the  latter.  The  lack  of  active  organic  matter  is  the  primary  cause 
of  soil  exhaustion.  Many  farmers  realize  its  value,  but  very  few 
have  made  any  definite  plans  for  its  permanent  maintenance.  To 
improve  a  worn-out  farm  is  not  an  easy  task.  Since  the  organic 
matter  for  our  soils  must  be  grown  on  our  farms,  the  first  require- 
ment is  that  the  soil  shall  be  in  condition  to  grow  it.  Legumes, 
and  more  especially  the  clovers,  are  the  best  crops  to  grow  for  soil 
improvement.  They  require  larger  amounts  of  minerals  in  the 
soil,  especially  calcium  and  phosphorus,  than  almost  any  other 
crop.  One  or  both  must  usually  be  supplied. 

1.  By  Addition  of  Limestone. — Many  soils  are  so  acid  or  sour 
that  the  best  soil-renovating  crops,  the  clovers,  will  not  grow  suc- 
cessfully. Before  these  soils  can  be  improved  to  any  extent,  unless 
an  unlimited  supply  of  manure  is  available,  limestone  must  be 
applied.  Many  experiments  have  shown  that  the  best  form  to  use 
is  ordinary  ground  or  crushed  limestone.  This  neutralizes  the 
acid,  prevents  leaching  of  organic  matter  and  furnishes  the  plant 
with  the  element  calcium. 

Limestone  is  rather  readily  soluble.  In  humid  regions  from 
500  to  800  pounds  are  leached  out  of  the  soil  each  year.  In  many 
158 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS        159 

soils  it  lias  been  so  completely  removed  that  they  are  acid  and  the 
element  calcium  is  too  deficient  to  produce  good  crops,  especially 
of  legumes.  Applications  should  be  made  once  in  every  rotation. 
To  maintain  the  limestone  at  present  prices  costs  from  fifty  cents 
to  one  dollar  per  acre  per  annum  pins  the  cost  of  applying  it. 
This  will  make  possible  the  growing  of  legumes  for  soil-renovating 
purposes.  On  eroded  hill  land  large  growths  of  sweet  clover 
amounting  to  2.7  tons  per  acre  for  the  two  years  of  its  growth 


Fio.  80. — Clover  on  gray  silt  loam  on  tight  clay.  (Marion  silt  loam.)  Manure  gave 
0.0  ton  of  gratis  with  practically  no  clover,  while  immure  with  rock  phosphate  ami  limestone 
gave  2.05  tons  of  good  clean  clover  hay.  (Illinois  Station.) 

were  made  possible  by  the  application  of  four  tons  of  limestone 
to  acid  soil. 

2.  By  Applications  of  Phosphorus. — Phosphorus  should  be 
mentioned  in  this  connection  because  so  many  soils  arc  deficient  in 
this  element,  and  its  application  is  very  necessary  for  increasing 
the  growth  of  legumes.  It  often  more  than  doubles  the  growth  of 
clovers  and,  of  course,  gives  a  larger  amount  of  much-needed  active 
material  to  be  turned  under.  The  acids  formed  in  the  decay  of 
organic  matter  aid  greatly  in  the  liberation  of  phosphorus  and 
potassium  that  are  locked  up  in  the  minerals  in  the  soil.  The 
average  increase  of  clover  at  the  Illinois  Station  at  Urbana  on 
brown  silt  loam  was  1.05  tons  per  acre  where  phosphorus  was  uscrl. 
while  on  another  field  on  the  same  type  the  increase  was  1.r>l  tons. 


160  SOIL  PHYSICS  AND  MANAGEMENT 

At  Fairfield,  in  southern  Illinois,  on  gray  silt  loam  on  tight  clay, 
Marion  silt  loam,  the  gain  for  phosphorus,  limestone  and  manure 
ovei  manure  alone  was  2.65  tons  per  acre  of  good  clover  hay.  All 
know  that  the  growing  of  large  legume  crops  aid  the  production  of 
large  crops  of  grain  (Fig.  80). 

3.  By  Accumulations  in  Pastures. — The  livestock  farmer  has 
one  decided  advantage  over  the  grain  farmer  in  that  some  of  his 
land  must  be  in  pasture  and  accumulations  of  organic  material 
are  taking  place  during  this  period  of  "rest."    A  large  amount  of 
the  organic  matter  that  grows  in  the  pasture  will  be  eaten  and  de- 
stroyed by  stock  in  the  process  of  digestion,  but  the  total  result 
will  be  beneficial  to  the  soil.     From  the  table  on  page  162  it  will 
be  seen  that  oftly  580  pounds  of  organic  matter  are  recovered  in 
the  manure  for  each  ton  of  pasture  grass  eaten  by  -stock.    For  red 
clover  pasture,  the  amount  is  680  pounds,  while  for  alfalfa  it  is  660 
pounds.     Pasture  grasses  develop  systems  of  roots  which  add  quite 
largely  to  the  organic  supply  in  the  soil.    If  legumes  can  be  grown 
in  connection  with  these  pasture  grasses  much  better  results  will  be 
secured  than  from  the  grass  alone.     In  the  case  of  sweet  clover 
growing  with  blue  grass,  it  is  found  that  the  amount  of  blue  grass 
will  be  larger  than  if  grown  alone.    In  pastures  there  is  very  little 
organic  matter  lost  by  oxidation,  since  this  process  is  not  very  act- 
ive in  sod,  there  being  no  more  nitrates  formed  than  are  used  by 
the  grass.    In  old  compacted  pastures,  nitrification  is  not  sufficiently 
rapid  to  maintain  a  good  growth  of  grass.     Farmers  speak  of  such 
pastures   as  being  "  sod  bound/'     Plowing  and  reseeding  or  at 
least  a  thorough  disking  may  be  necessary  to  completely  aerate 
the  soil  and  bring  about  larger  growth. 

Pasture  grasses  are  frequently  eaten  so  closely  by  stock  that 
very  little  benefit  is  derived  by  the  soil.  Clover  is  often  pastured 
so  that  at  the  end  of  the  season  there  is  nothing  left  on  the  ground 
to  turn  under  for  soil  improvement. 

4.  Green  Manures. — One  of  the  very  important  ways  of  in- 
creasing the  organic  matter  is  by  the  use  of  green  manures.    Almost 
any  crop  may  be  used  for  this  purpose,  but  legumes  are  much  better 
because  of  the  greater  value  of  the  material  for  soil  improvement. 
The  crop  selected  should  depend  upon  the  time  of  planting,  the 
period  available  for  growth,  the  character  of  the  soil  to  be  im- 
proved, and  the  system  of  farming  practiced.     The  legumes  best 
adapted  to  single  summer  growth  are  cowpeas,  soybeans,  common 
vetch,  field  peas,  and  velvet  beans.     Red,   sweet  and  mammoth 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS        161 

clovers  are  biennials  and  can  be  seeded  one  year  with  a  nurse  crop 
and  allowed  to  produce  a  growth  the  ne.xt  spring  before  turning 
under.  Hairy  or  winter  vetch  may  be  seeded  with  rye  or  winter 
oats  for  early  spring  pasture  and  plowed  under  for  corn,  cotton  or 
other  crops.  It  is  a  common  practice  in  the  corn  belt  to  sow  clover 
with  wheat,  oats  or  rye  and  turn  it  under  in  the  fall  or  the  fol- 
lowing spring  for  corn.  Sweet  clover  is  excellent  for  this  purpose 
in  many  localities.  One  to  two  tons  of  dry  material  have  been 
turned  under  in  time  for  the  corn  crop  without  apparent  injury. 
There  is  danger,  however,  from  plowing  under  a  large  amount  of 
green  material  to  be  followed  by  a  crop  of  corn,  cotton,  or  potatoes. 
During  the  last  few  years  some  complete  failures  have  resulted  from 
this  practice.  The  green  crop  takes  out  much  of  the  available 
plant  food  and  moisture  and  may  leave  the  soil  so  deficient  in  these 
that  the  crop  which  follows  may  be  seriously  injured.  Besides,  the 
fermentation  of  the  green  material  may  develop  heat  that  will  drive 
off  some  moisture  and  leave  the  soil  still  drier,  although  the  large 
amount  of  water  turned  under  with  the  green  crop  would  tend  to 
compensate  for  any  lost  in  this  way. 

5.  Catch  and  Cover  Crops. — Many  times  it  is  advantageous 
to  use  crops  for  some  'special  purpose  in  which  no  attempt  is  made 
to  grow  them  to  maturity.     Legumes,  rye,  oats  or  other  crops  are 
sometimes  sown  on  laiid  that  is  to  lie  idle  for  a  time  in  order  to  use 
the  available  nitrates   and  prevent  their  loss   by  leaching.     This 
plan  rs  especially  advisable  on  sandy  soils,  but  it  may  be  applied 
to  other  soils  to  good  advantage.     Wheat  on  sandy  land  could  be 
immediately    followed   by   cowpeas,   which    not  only    conserve   the 
nitrates  but  add  nitrogen  to  the  soil.     Wheat  and  oats  on  heavier 
soils,  such  as  silt  and  clay  loams,  are  usually  followed  soon  after 
harvest  by  a  crop  of  weeds  and  grass  which   act  as  very  efficient 
catch   crops.     Wherever  possible   legumes   should    be  grown   after 
oats,  wheat,  or  barlev  for  this  purpose  because  of  their  double  value. 
Cow-peas,  soybeans  or  clover  are  sometimes  seeded   in  corn   at  the 
last  cultivation  to  be  used  as  a  soil-improving  catch  crop.     They 
may  also  be  seeded  in  the  hill  of  corn  without  serious  detriment 
to  the  corn.     Kape.  cowhorn  turnips,  or  rye  may  be  used  as  catch 
crops.     These  may   be   pastured    and    thus   acquire   an    additional 
value. 

The  same  crops  may  he  n-spd   as  cover  crops  in   orchards   to 
hasten  the  maturity  of  wood  or  on  hillsides  to  prevent  washing. 

6.  Barnyard  Manures. — Manure  is  one  of  the  most  valuable 
11 


162 


SOIL  PHYSICS  AND  MANAGEMENT 


by-products  of  the  farm;  however,  sufficient  manure  cannot  be 
produced  from  the  crops  grown  on  the  farm  to  maintain  the  supply 
of  organic  matter.  This  is  due  to  the  fact  that  a  large  amount  of 
the  organic  matter  is  destroyed  during  the  process  of  digestion. 

Average  Digestibility  of  Some  Common  Feeds  l 


Feeds 

Dry  matter 
digested 

Dry  matter  recovered 
in  manure 

Pasture  grasses  

per  cent 

71 
66 
67 
61 
61 
60 
48 
43 
60 
63 
79 
64 
70 
91 
61 

per  cent 

29 
34 
33 
39 
39 
40 
52 
57 
40 
37 
21 
36 
30 
9 
39 

poundg  per  ton 

580 
680 
660 
780 
780 
800 
1040 
1140 
800 
740 
420 
720 
600 
180 
780 

Red  clover,  green  

Alfalfa,  green  

Mixed  meadow  hav  

Red  clover  hay  ... 

Alfalfa  hay         

Oat  straw  

Wheat  straw     

Corn  stover          

Shock  corn                               .  .    . 

Corn-and-cob  meal  

Corn  ensilage  

Oats  

Corn  

Wheat  bran  

From  the  above  table  it  is  seen  that  in  feeding  hay  about  40  per 
cent  of  the  organic  matter,  or  800  pounds  per  ton  of  hay  fed,  is 
recovered  in  the  manure,  while  with  pasture  grasses  an  average  of 
32  per  cent,  or  640  pounds  per  ton,  is  recovered.  In  the  feeding  of 
straw,  shock  corn  or  even  ensilage,  the  animals  leave  a  considerable 
amount,  so  that  somewhat  more  organic  matter  is  recovered  than 
indicated  by  the  figures. 

The  amount  and  composition  of  manure  produced  by  different 
animals  vary  quite  widely.  The  following  table  gives  the  amount: 

Amount  and  Value  of  Manure,  Solid  and  Liquid,  Excreted  by  Various  Farm 
Animals  per  1000  Pounds  of  Live  Weight 


Animal 

Pounds  * 
per  day 

Average  * 
tons  per  year 

Per  cent  * 
solid 

Per  cent  * 
liquid 

Value  » 

Horse  

35-45 

7.0 

80 

20 

$19.88 

Cow  

70-80 

12.7 

70 

30 

28.07 

Steer  

40-50 

7.5 

70 

30 

21.75 

Swine  

40-50 

7.3 

60 

40 

25.48 

Sheep  

30-40 

5.5 

67 

33 

32.06 

Tn  connection  with  this,  attention  is  called  to  the  next  table, 
which  gives  the  composition  of  the  manure: 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS        163 
Composition  of  Fresh  Manure  4 


Animal 

Excrement 

Water             Nitrogen 

Phosphorus 

Potassium 

per  cent 

per  cent 

per  cent 

per  cent 

per  cent 

Solid     80 

75 

.55 

.13 

.33 

Horse 

Liquid  20 

90 

1.35 

Trace 

1.03 

Mixed   .  . 

78 

.70 

.11 

.45 

Solid     70 

85 

.40 

.09 

.08 

Cow 

Liquid  30 

92 

1.00 

Trace 

1.11 

Mixed    .  . 

80 

.60 

.07 

.37 

Solid      60 

80 

.55 

22 

.33 

Swine 

Liquid  40 

97 

.40 

.05 

.37 

Mixed    .  . 

87 

.50 

.15 

.37 

Solid     67 

60 

.75 

.22 

.37 

Sheep 

Liquid  33 

85 

1.35 

.02 

1.74 

Mixed    .  . 

68 

.95 

.15                  .83 

7.  Loss  of  Manure  and  its  Prevention. — A  source  of  great 
loss  occurs  in  the  handling  of  manure  after  it  is  produced.  In  too 
many  cases  it  is  left  in  the  lot  or  under  the  eaves  of  the  barn 
or  shed  until  the  organic  matter  is  decomposed  and  a  large  amount 
of  the  fertility  is  carried  away.  In  the  process  of  rotting  there  is  a 
large  amount  of  organic  matter  lost.  To  determine  the  amount 
of  loss  the  Ontario  Station  placed  four  tons  of  mixed  cow  and 
horse  manure  in  equal  amounts  in  a  protected  shed  and  a  like 
amount  in  an  open  bin  exposed  to  the  weather.  The  four  tons 
contained  1!)38  pounds  of  organic  matter.  The  losses  are  given 
in  the  next  table. 

Loss  of  Organic  Matter  awl  Fertility  in  the  Rotting  of  Manure  • 


Fresh 

At  the  end  of 
three  months 

At  the  end  of 
six  months 

At  the  end  of 
nine  months 

At  the  end  of 
twelve 
months 

Pro-  i    Ex- 
torted posed 

Pro-   !    Ex- 
torted posed 

Pro- 
tected 

Ex- 
posed 

Pro- 
tect ed 

Ex- 
posed 

Pro-  1    Ex- 
tected  posed 

Weight  of  manure 
Weight  of  organic 
matter 

pound* 
SOOO   SOOO 
193S    1938 

pnuniis 

29SO  ,  3903 
880     791 

POM 
230S 
803 

nds 

4124 
652 

ptiuiulx 

2224   41S9 
760     648 

pnunds 

215S:3S3S 
770     607 

Loss  in  per  cent 

Organic  matter.  . 

55      <»0 
17      29 
None     3.5 
None   It) 

58 
19 
Xom 
2 

65 

30 
5.2 
21 

60 

23 

None 
2 

67 
40 

5.7 
24 

60        69 
23     1    40 
1.7        7 
2         25 

Nitrogen  

Phosphorus.  . 

Potassium 

164  SOIL  PHYSICS  AND  MANAGEMENT 

It  is  very  important  that  the  manure  should  be  handled  in  such 
a  way  as  to  lose  as  little  as  possible.  The  best  plan  is  to  scatter 
it  on  the  land  as  soon  as  practicable  after  it  is  produced.  If  the 
fertility  is  leached  out  then  it  goes  into  the  soil,  and  if  the  manure 
becomes  dry  there  is  essentially  no  loss.  The  farm  should  be  man- 
aged, if  possible,  so  there  would  always  be  a  place  to  haul  manure. 
If  this  is  not  feasible  under  the  system  followed  or  if  the  fields  be- 
come too  wet  to  draw  the  manure  upon  them,  the  problem  of  pre- 
venting loss  becomes  an  important  one.  It  is  well  to  remember 
that  the  greatest  losses  are  due  to  fermentation  and  leaching. 

(a)  Fermentation. — The  process  of  fermentation  is  largely  re- 
sponsible for  loss  of  nitrogen  and  organic  matter.    It  is  practically 
impossible  to  prevent  it  entirely,  but  it  should  be  reduced  to  a 
minimum.    When  manure,  particularly  from  horses,  is  thrown  into 
a  pile  it  soon  begins  to  heat.    This  indicates  that  bacterial  action 
or  fermentation  is  taking  place.   The  organic  matter  of  the  manure 
is  being  decomposed  and  nitrogen  in  the  form  of  ammonia  is  given 
off,   resulting  in  large  losses.     In  connection  with  this  process, 
other  organisms  may  work,  causing  "  fire  fanging,"  resulting  in 
a  light,  powdery  form  of  manure  of  little  value.     A  process  of 
fermentation  takes  place  in  cow  manure  or  compact  manures  that 
results  in  rotting  without  so  much  loss.     This  is  known  as  putre- 
faction and  is  due  to  anaerobic  bacteria  or  those  working  without 
oxygen.    The  fermentation  may  be  largely  prevented  by  excluding 
the  air,  since  oxygen  is  necessary  for  the  process.    This  may  be  done 
in  two  ways,  first  by  allowing  stock  to  trample  the  manure,  thus 
compacting  it  so  much  as  to  exclude  the  air,  and,  second,  keeping 
the  manure  very  wet. 

(b)  Leaching. — The  greatest  loss  of  manure  is  due  to  leaching, 
as  .it  affects  all  constituents  and  elements  alike.   The  colored  liquid 
draining  from  the  manure  heap  carries  large  amounts  of  valuable 
material  away  in  the  drainage  waters.     The  Ohio  Station  found 
that  manure  from  steers  exposed  for  three  months,  January  to 
April,  decreased  in  plant  food  value  per  ton  from  $3.01  to  $1.85,  or 
there  was  a  loss  of  $1.16,  or  38.6  per  cent.     The  loss  of  organic 
matter  was  fully  as  great.    Leaching  may  be  prevented  by  keeping 
the  manure  in  a  shed  to  protect  it  from  the  rain.     Tf  exposed,  it 
should  be  kept  in  a  concrete  pit  or  tank  to  prevent  loss  by  leaching 
and  very  wet  to  prevent  heating.     Horse  manure  is  the  most  diffi- 
cult to  keep  because  of  its  tendency  to  heat,  owing  to  its  looseness 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS       165 

and  the  free  access  of  air.     Where  possible  it  should  be  mixed  with 
cow  manure  to  render  it  more  compact. 

It'  the  animals  are  being  fed  in  a  shed  or  barn  where  the  manure 
may  be  left  till  it  is  hauled  out  there  will  be  less  loss  than  in  any 
other  way.  If  a  cement  floor  is  used  there  will  he  no  loss  by  leach- 
ing and  the  tramping  of  stock  will  exclude  the  air  so  that  very  little 

FIG.  81. 


-it 


Fia.  81. — How  (loos  this  man  handle  manure-?     The  stains  answer  the  question. 
Fio.   S2. — When  the  spreader  is  filled  the  manure  is  hauled  to  the  field.      In  this  way  there 

is  very  little  loss. 

fermentation  will  take  place.  Various  experiment  stations  have 
demonstrated  the  higher  value  of  manure  and  the  lower  loss  when 
kept,  in  this  way.  Compare  figures  81  and  8X\ 

(c)  Absorbents. — Substances  that  act  as  absorbents  of  ammonia 
and  other  constituents  that  would  he  removed  easily  are  sometimes 
mixed  with  the  manure.  Dry  earth  or  dry  peat  may  be  used  to 


166 


SOIL  PHYSICS  AND  MANAGEMENT 


good  advantage.  Calcium  sulfate,  laud  plaster,  may  be  dusted 
over  the  manure.  The  sulfuric  acid  unites  with  the  ammonia, 
forming  ammonium  suifate,  which  is  comparatively  slowly  soluble, 
Common  salt  is  sometimes  used,  but  both  it  and  land  plaster  are  too 
expensive  for  general  use. 

Certain  substances  may  be  used  as  absorbents  and  also  for  re- 
enforcing  the  manure.  If  the  manure  is  to  be  used  on  land  de- 
ficient in  the  element  potassium,  kainit  may  be  used  for  this  pur- 
pose and  when  the  manure  is  scattered  over  the  land  will  supply  the 
needed  element.  Finely  ground  rock  phosphate  or  floats  may  be 
used  as  an  absorbent  and  at  the  same  time  supply  the  element  phos- 
phorus, in  which  most  soils  are  deficient.  At  the  Ohio  Station  the 
average  annual  increase  for  stall  manure  and  floats  over  stall  manure 
alone  was  7.2  bushels  of  corn  per  acre,  while  the  increase  for  yard 
manure  treated  over  untreated  was  6.4  bushels.  The  corresponding 
increases  for  wheat  were  4.1  and  3.4  bushels  per  acre. 

The  next  table  shows  the  amount  of  loss  from  manure  with 
absorbent  reenforcement  exposed  for  three  months.  The  experi- 
ments were  made  at  the  Ohio  Station. 

Composition  of  Steer  Manure  After  Exposure  for  Three  Months — Pounds 

Per  Ton 6 


Treatment 

Organic 
matter 

Ash 

.Nitro- 
gen 

10.70 
7.46 
30.28 

Phos- 
phorus 

8.60 

7.57 
11.97 

Potas- 
sium 

7.38 

3.52 
52.30 

Floats  =  Rock        Pounds  at  beginning 
phosphate          Pounds  at  end 
Per  cent  of  loss 

349.00 
310.74 
10.96 

120.20 
98.95 
17.67 

Acid  phosphate     Pounds  at  beginning 
Pounds  at  end 
Per  cent  of  loss 

357.80 
269.89 
24.57 

101.40 
85.88 
15.30 

9.86 
7.18 
27.18 

5.70 
4.79 
15.96 

6.88 
2.99 
56.54 

Pounds  at  beginning 
Kainit                   Pounds  at  end 
Per  cent  of  loss 

369.00 
291.50 
21.00 

107.40 
83.64 
22.12 

9.76 
6.68 
31.56 

2.88 
2.48 
13.89 

10.70 
4.98 
53.46 

Pounds  at  beginning 
Gypsum                Pounds  at  end 
Per  cent  of  loss 

375.40 
267.35 

28.78 

104.60 

75.72 
27.61 

9.68 
7.94 
17.97 

2.76 
2.66 
3.63 

7.86 
2.56 

67.42 

Pounds  at  beginning 
Untreated              Pounds  at  end 
Per  cent  of  loss 

416.00 
254.79 
38.75 

79.20 
65.68 
17.07 

10.30 
7.18 
30.29 

3.24 
2.47 
23.76 

8.14 
3.35 

58.84 

The  value  of  manure  in  a  soil  depends  upon  three  things: 
first,  the  beneficial  physical  effect  produced ;  second,  the  plant  food 
supplied,  and,  third,  the  stimulus  given  to  bacterial  activity.  Its 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS        167 

real  value  to  the  farmer  can  be  determined  only  by  the  money 
returns  secured  from  increased  yields.  This  depends  upon  several 
factors:  the  soil  itself,  the  crop  grown,  the  price  received  for  the 
crop,  the  rate  of  application  and  the  cost  of  the  manure. 

As  a  general  rule  the  better  the  soil  the  less  need  there  is  for 
manure  and  the  smaller  the  returns  per  ton  from  its  use.  The 
poorer  the  soil  the  greater  the  need  and  the  larger  the  returns. 
Farmers  recognize  this  fact  and  usually  apply  manure  to  the  poorer 
place.-;  on  their  farms. 

All  crops  do  not  respond  equally  well  to  manure.  Its  value 
may  be  increased  by  applying  to  the  right  crop.  Timothy,  corn 
and  wheat  usually  give  good  returns  from  applications  of  manure, 


Fio.  83. — Manure  spreader  in  action.     The  manure  is  torn  apart  so  aa  to  be  scattered  uni- 
formly.     (J.  C.  Beavers,  Cir.  49  Purdue  Station.) 

yet  corn  may  be  a  complete  failure  after  manure.  This  is  not 
usually  the  fault  of  the  manure,  but  of  the  amount  applied  and 
subsequent  management.  Strawy  manure  plowed  under  late  in 
the  spring  without  disking  is  very  likely  to  injure  corn  because  of 
the  effect  on  moisture  movement. 

The  common  impression  is  that  heavy  applications  of  manure 
are  most  profitable.  The  greatest  profit,  per  ton  of  manure  is  ob- 
tained from  light  applications  when  well  distributed.  This  may 
best  be  accomplished  with  the  manure  spreader.  At  the  Ohio  Sta- 
tion at  Woostor  an  average  of  twenty  years  shows  a  valuo  of  $3. -18 
per  ton  where  four  tons  of  manure  were  applied.  $2.70  with  8  tons 
and  $2.24  with  lf>  tons  per  acre. 


168 


SOIL  PHYSICS  AND  MANAGEMENT 


The  following  table  gives  data  from  Purdue  Station  and  illus- 
trates the  value  of  different  amounts : 

Average  Value  of  Increase  for  Manure  Per  Crop  and   Per  Ton  for  Twenty-three 

Years,  1890-1912  1 


Rotations 

Average  amount  in 
tons  per  rotation 

Value  of  increase 

Corn  

heavy] 
1424 

light 
8.8 

heavy 

$3.11 
4.78 
5.83 
4.91 
1.31 
8.55 
4.98 
7.33 
1.39 
8.16 
11.45 
1.79 
6.79 
1.02 
6.17 
1.42 
1.39 

liaht 
$3.78 
4.03 
4.52 
3.90 
1.84 
6.68 
4.28 
5.53 
1.81 
6.81 
9.33 
2.40 
6.38 
1.67 
5.25 
1.93 
1.93 

Oats  

Wheat  

Clover  

Average  per  ton  of  manure      

Corn  

1500 

9.1 

Oats  

Wheat  

Average  per  ton  of  manure  

Com  

1094 

6.72 

Wheat  

Average  per  ton  of  manure  

Corn  continuously      .            

661 

3.81 

Average  per  ton  of  manure  

Wheat  continuously                   

435 

2.72 

Average  per  ton  of  manure  

Average  per  ton  of  manure  for  all 
experiments 

(d)  Methods  of  Applying  Manure. — For  an  application  of 
manure  to  be  most  effective  it  should  be  evenly  distributed  and 
then  thoroughly  mixed  with  the  soil.  It  is  very  difficult  to  accom- 
plish the  first  by  hand  spreading.  There  will  almost  certainly  be 
large  chunks  of  manure  alternating  with  bare  spots.  The  manure 
spreader  (Fig.  83)  is  indispensible  for  this  purpose.  It  tears  the 
manure  to  pieces,  scatters  it  evenly  and  permits  of  smaller  applica- 
tions. The  same  amount  of  manure  covers  a  larger  area  and,  as 
seen  from  the  above  table,  gives  it  a  higher  value  per  ton.  The 
mixing  of  the  manure  with  the  soil  may  be  readily  accomplished 
by  the  disk.  This  is  not  so  important  unless  a  crop  is  to  follow 
soon,  as  in  the  case  of  spring  plowing  for  corn  or  summer  plowing 
for  wheat.  It  is  especially  desirable  for  coarse  manures  which  when 
plowed  under  interfere  with  capillary  movement. 

The  manure  should  be  applied  as  soon  as  possible  after  being 
produced,  since  there  is  less  loss  when  in  or  on  the  soil  than  if  left 
in  the  lot  or  even  the  shed  (Fig.  82).  Some  farmers  prefer  well 
rotted  manure,  but  there  is  too  much  loss  in  the  process  of  decay  to 
allow  this  to  go  on  in  any  other  place  than  in  the  soil.  Weight  for 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS        169 

weight,  well  rotted  manure  may  be  more  valuable  -than  fresh 
manure,  but  the  loss  of  fertility  and  organic  matter  involved  in  the 
process  more  than  overbalances  the  benefits.  The  character  of  the 
rotted  manure  will  depend  upon  the  conditions  under  which  the 
decay  took  place.  There  is  no  question  but  that  twenty  tons  of 
fresh  manure  applied  to  soil  will  produce  greater  increase  than 
the  same  weight  of  manure  would  after  it  is  well  rotted.  In  many 
cases  it  is  not  practical  to  apply  manure  as  rapidly  as  produced. 
Farmers  of  the  corn  belt  haul  out  the  manure  in  summer  and 
early  spring.  That  taken  out  in  'summer  is  usually  placed  on  land 
to  be  fall  plowed.  This  is  without  doubt  a  good  practice.  The 
manure  becomes  decayed  sufficiently  by  spring  so  that  it  will  not 


Fio.  84. — An  expensive  and  wasteful  way  of  handling  manure  on  the  farm.     Do  not  put 
it  in  piles.     (Deere  &  Co.) 

interfere  with  moisture  movement.  The  fall  and  winter  loss  is 
avoided. 

Coarse  manure  is  best  applied  in  the  fall,  but  if  the  applica- 
tion is  made  in  spring  it  should  be  very  light.  Heavy  spring  appli- 
cations may  ruin  the  crop,  especially  corn.  In  the  dry  summer  of 
1914  corn  on  some  fields  that  had  received  heavy  applications  of 
manure  before  being  plowed  in  the  spring  produced  no  grain 
whatever. 

Manure  is  sometimes  piled  in  the  field  in  small  heaps  and  later 
scattered  with  the  fork.  This  is  not  only  an  expensive  but  a 
wasteful  process.  Much  of  the  fertility  is  leached  into  the  soil 
beneath  the  heaps  and  a  large  amount  of  manure  is  left  at  these 
spots  in  spreading  (Fig.  84).  The  result  is  a  great  many  very 
rich  spots  upon  which  small  grain  lodges  badly  and  is  frequentlv 


170 


SOIL  PHYSICS  AND  MANAGEMENT 


lost.     These  spots  are  still  visible  in  oats  after  25  years  011  a  1'arin 
in  the  vicinity  of  the  University  of  Illinois. 

8.  Organic  Residues  of  the  farm  are  of  two  kinds,  those  that 
form  no  part  of  the  crop,  as  weeds,  and  those  that  are  part  of  the 
crop  or  harvested  with  the  crop,  such  as  corn  stalks,  straw  and 
stubble.  Heretofore  it  has  been  believed  by  many  farmers  that 
most  crop  residues  have  little  or  no  value  and  the  easiest  way  of 
disposing  of  them  was  the  best;  consequently  much  material  wa--' 
burned  and  the  practice  has  by  no  means  ceased.  It  is  estimated 


Fio.  85. — Burning  corn  stalks — In  addition  to  the  organic  matter  destroyed  in  burning  the 
stalks  some  organic  matter  in  the  soil  is  burned. 

that  in  the  western  part  of  the  United  States  the  straw  from  20,000,- 
000  to  30,000,000  acres  of  grain  is  burned  every  year,  while  in  the 
corn  belt  the  practice  of  burning  stalks  is  still  somewhat  prevalent  in 
certain  sections  (Fig.  85).  This  enormous  waste  of  organic  mat- 
ter and  nitrogen  is  to  be  regretted  very  much.  Crop  residues  of 
all  kinds  have  great  value.  Chemists  tell  us  that  straw  has  a 
manurial  value  of  $2  to  $3  per  ton,  over  half  of  which  is  due  to 
the  plant  food  which  it  contains,  while  the  rest  is  due  to  the  physical 
effect  upon  the  soil.  Corn  stalks  contain  Ifi  pounds  of  nitrogen  per 
ton,  and  even  after  exposure  during  the  winter  the  amount  is  re- 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS       171 

duced  only  about  iy2  pounds,  so  that  the  burning  of  corn  stalks 
results  in  a  loss  of  14  y2  pounds  of  nitrogen  per  ton,  which  at  15 
cents  a  pound  would  amount  to  $2.17.  There  is  little  doubt  but 
that  the  value  of  the  corn  stalks  for  improving  the  tilth  would  be 
equal  to  one-half  of  the  value  of  the  nitrogen,  so  that  for  turning 
back  into  the  soil  the  corn  stalks  are  worth  fully  $3  per  ton.  The 
value  of  residues  is  shown  in  the  yields  secured  where  they  have 
been  returned  to  the  soil  for  a  number  of  years. 

One  of  the  most  valuable  crop  residues  is  that  from  legumes, 
which  are  frequently  grown  for  the  seed  and  the  straw  returned 
to  the  soil.  It  furnishes  organic  matter  in  its  most  active  form, 
rich  in  nitrogen,  and  its  rapid  decomposition  makes  it  one  of  the 
best  amendments  for  soils  in  bad  physical  condition. 

On  the  experiment  field  at  Bloommgton,  Illinois,  where  crop 
residues  had  been  turned  under  for  five  years,  the  yield  of  wheat 
for  1911  was  increased  4.4  bushels  over  that  where  the  crop  residue? 
had  been  removed,  and  in  1912  the  yield  of  corn  was  increased  7.9 
bushels  and  in  1913,  5.9  bushels.  At  the  experiment  field  at  Du  Bois, 
Illinois,  crop  residues  turned  under  gave  an  increase  of  $19.28  * 
for  twelve  crops,  or  $1.61  per  acre  annually,  while  with  phos- 
phorus applied  the  increase  for  residues  was  $40  for  the  twelve 
crops,  or  $3.33  per  acre. 

The  turning  under  of  crop  residues  on  the  grain  farm  in  the 
corn  belt  is  very  essential,  since  it  is  the  only  means  the  grain 
farmer  has  of  maintaining  the  organic  matter.  If  he  makes  use  of 
residues  and  an  occasional  crop  of  clover  he  has  even  a  better 
chance  of  maintaining  the  organic  matter  than  the  stock  farmer 
who  loses  so  much  organic  matter  during  the  process  of  feeding. 
(See  the  table  page  1(>2.) 

9.  Growing  Non-Tilled  Crops. — Tillage  increases  oxidation  of 
organic  matter  by  bringing  about  favorable  conditions  of  moisture 
and  aeration.     The  compact  condition  of  the  soil  where  non-tilled 
crops  are  grown  retards  decomposition  of  organic  matter,  hence 
the  benefit  of  such  crops  as  wheat,  oats,  rye,  barley  and  grasses. 

10.  Rotation  of  Crops. — dotation  permits  the  growing  of  tilled, 
non-tilled  and  soil-renovating  crops.      Farmers  should  plan  their 
rotations  with  the  thought  of  soil   maintenance.     This  is   funda- 
mental.    The  length  of  the  rotation  and  crops  selected  should  be 
adapted  to  the  soil  and  to  the  system  of  farming.     On  soils  well 

'The  price  of  porn  wa<*  figured  at  35  rents  per  bushel,  oats  at  30  eents, 
wheat  at  70  cent's,  eloverseed  at  $«!  and  soyl>eans  at  $1   per  hnshel. 


172 


SOIL  PHYSICS  AND  MANAGEMENT 


supplied  with  organic  matter  the  rotation  should  be  quite  different 
from  that  on  soils  deficient  in  this  constituent.  In  the  former 
case  much  of  the  residues  might  be  sold  from  the  farm,  while  in 
the  latter  much  the  larger  part  should  be  returned  to  the  soil.  One 
essential  of  a  rotation  for  soil  improvement  is  at  least  one  legume 
crop  during  the  cycle.  Soils  deficient  in  organic  matter  should 
have  a  more  frequent  recurrence  of  this  crop,  as  the  value  of  the 
rotation  in  improving  the  soil  depends  primarily  on  the  use  of  it. 
The  legume  should  be  turned  back  into  the  soil  whenever  possible. 
If  it  is  removed  and  nothing  returned  in  its  place  very  little  or 
nothing  is  gained  for  permanent  soil  improvement  and  maintenance. 
f  '  " 


Fid.  86. — Adding  organic  matter  to  the  soil  in  the  form  of  sweet  clover. 

Clover  and  cowpeas  are  commonly  grown.  The  best  one  to  grow 
on  the  grain  farm  is  that  which  provides  the  largest  amount  of 
material  to  turn  under.  Medium  red  clover  is  most  common  in  the 
northern  states,  but  alsike  or  sweet  clover  is  better  adapted  to 
somewhat  poorly  drained  soils.  Mammoth  or  English  and  sweet 
clover  probably  furnish  the  largest  amount  of  material  to  plow 
under,  and  both  plants  will  furnish  a  fair  crop  of  seed,  upon  which 
the  farmer  must  depend  for  his  immediate  returns.  It  requires 
the  very  best  conditions  for  red  clover  to  produce  three  tons  per 
acre  for  both  crops,  which  is  at  least  one  ton  above  the  average. 
Sweet  clover  is  an  excellent  legume  for  soil  improvement  because  of 
its  large  growth  (Fig.  86)  and  deep  rooting  characteristics. 


MAINTAINING  THE  ORGANIC  MATTER  OF  SOILS       173 

The  following  table  gives  the  amount  that  has  heen  produced 
during  the  two  years'  growth  : 

Investigation  of  Sweet  Clover  (Melilotus  alba)* 


Parts  of  plant 

Depth 

(inches) 

Dry  matter  per  acre 

N'itrogen  per  acre 

Pounds 

Per  cent 
of  total 

Pounds 

Per  cent 
of  total 

Total  tops     ! 

10367 
1809 

601 

81 

14 
5 

197 
22 

J 

31 

228 

86 

10 
4 

Total  surface  roots  

Oto    7 
7  to  20 

Oto  20 

Subsurface  roots  

Total  roots  

2410 
12777 

19 

100 

14 
100 

Total  tops  and  roots 

From  the  above  table  it  will  be  seen  that  the  sweet  clover  pro- 
duced G.4  tons  of  total  dry  matter.  Of  this  1.2  tons  came  from 
the  roots.  The  total  weight  of  sweet  clover  from  a  single  year's 
growth  in  the  dry  season  of  1914  on  black  clay  loam  was  4.4  tons 
per  acre. 

QUESTIONS 

1.  Would  it  be  advisable  to  purchase  manure  for  ordinary  crops? 

2.  What  is  the  first  requirement  in  maintaining  organic  matter? 

3.  Why  is  it  necessary  to  add  limestone? 

4.  What  is  the  cost  of  maintaining  it? 

5.  What  is  the  effect  of  phosphorus  on  growth  of  clovers? 

(5.  What  advantage  does  the  livestock  farmer  have  over  the  grain  farmer? 

7.  How  much  organic  matter  is  lost  in  the  process  of  digestion  of  pasture 

grasses?     Of  alfalfa? 

8.  What  is  the  remedy  for  "  sod  Ixiund  "  pastures? 
0.  Why  is  pasturing  often  of  little  benefit  to  soils? 

10.  What  points  should  l>e  considered  in  selecting  a  crop  for  green  manure? 

11.  (Jive  danger  to  crop  arising  from  green  manure  turned  tinder  in  spring. 

12.  What  are  catch  crops?     For  what  used? 

13.  Explain  under  what  conditions  weeds  may  have  some  value. 

14.  What  is  the  use  of  cover  crops? 

15.  In  pasturing  red  clover  what  per  cent  of  the  organic  matter  is  lost? 
Hi.  What  proportion  of  the  corn  fed  is  recovered  in  the  manure? 

17.  If  a  farmer  keeps   10  horses   averaging    1400   pounds  each.  .">  cows  of 

800  pounds  and  10  hogs  of  100  pounds  each,  what  is  the  value  of  the 
manure  produced  in  a  year? 

18.  What  are  the  sources  of  loss  of  manure? 

10.  Give  the  experiment  conducted  by  the  Ontario  Station. 

20.  Why  is  there  no  loss  from  dry  manure? 

21.  What  is  "  fire  fanging'1? 

22.  What  is  putrefaction? 

23.  How  may  fermentation  be  prevented? 

24.  What  parts  of  manure  are  affected  by  fermentation? 


174  SOIL  PHYSICS  AND  MANAGEMENT 

25.  What  portions  are  affected  by  leaching? 

26.  What   was   determined   in    regard   to   loss   from   manure   by   the   Ohio 

Station  ? 

27.  What  is  the  best  way  to  keep  manure  to  prevent  loss? 

28.  What  are  absorbents  ?     Name  some. 

29.  What  are  the  uses  of  reenforcing  materials  ? 

30.  Upon  what  does  the  value  of  manure  depend? 

31.  How  may  its  real  value  be  determined?     Upon  what  does  this  depend? 

32.  On  what  kind  of  soil  should  manure  be  applied  ? 

33.  What  crops  respond  best  to  manure? 

34.  What  amounts  of  manure  are  test  to  apply? 

35.  Give  the  results  obtained  by  the  Purdue  Station. 

36.  What   are   the   advantages   to   be   gained    by   the   use   of   the   manure 

spreader  ? 
37'.  Wrhat  is  the  value  of  corn  stalks  and  straw  ? 

38.  What  increases  have  been  obtained  by  the  use  of  crop  residues? 

39.  What  is  the  advantage  of  growing  non-tilled  crops? 

40.  What  is  essential  in  a  rotation  for  soil  improvement? 

41.  How  should  the  legume  be  managed? 

42.  Which  legumes  are  best  for  soil  improvement  ? 

43.  What  was  the  total  amount  of  organic  matter  produced  by  a  single 

season's  growth  of  sweet  clover? 

REFERENCES 

1  Hopkins,  C.  G.,  Soil  Fertility  and  Permanent  Agriculture,  1910,  p.  201. 
1  Beavers,  J.  C.,  Circular  49,  Purdue  Station,  Farm  Manures,   1915,  p.   3. 

*  Van  Slyke,  L.  L.,  Fertilizers  and  Soils,  1915,  p.  291. 
4  Op.  Cit.,  p.  291. 

•  Ontario  Station. 

•Thome,  C.  E.,  Farm  Manures,  1914,  p.  148. 

7  Circular  49,  Purdue  Station,  p.  14. 

•Hopkins,  C.  G.,  Soil  Fertility  and  Permanent  Agriculture,  1910,  p.  220. 


CHAPTER    XIII 


PHYSICAL   PROPERTIES    OF   SOILS 

1.  Real  or  Absolute  Specific  Gravity. — The  real  specific 
gravity  of  soils  varies  with  the  kind  and  amount  of  minerals  com- 
posing them  and  the  amount  of  organic  matter  present.  The 
specific  gravity  of  some  of  the  more  important  minerals  in  soils  is 
given  in  the  following  table: 

Specific  Gravity  of  Soil-Forming  Minerals 


Quartz I  2.65 

Albite ;  2.61 

Orthoclase 2.56 

Oligoclase 2.60 

Labradorite 2.68 

Anorthitc 2.72 

Dolomite 2.85 

Limonite !  3.6  to  4.0 

Magnetite '  5.0  to  5.1 

Zeolites...  2.25 


Kaolinite 2.50 

Amphibole 2.9  to  3.4 

Pyroxene 3.2  to  3.5 

Muscovite 2.7  to  3.0 

Biotite 27  to  3.1 

Calcite 2.70 

Gypsum 2.33 

Hematite 4.5  to  5.3 

Epidote 3.25  to  3.5 


Organic  matter  is  the  lightest  soil  constituent,  its  specific  gravity 
being  1.2  to  1..3.  The  specific  gravity  of  the  surface  soil  of  brown 
silt  loam,  the  common  prairie  soil  of  the  corn  belt,  is  2.(>'2,  of  gray, 
yellow  gray,  or  yellow  silt  loam  2.(>5,  while  of  black  clay  loam  it 
'is  2.57. 

2.  Apparent  Specific  Gravity. — The  real  specific  gravity  is  of 
very  little  importance  in  comparison  with  the  apparent  specific 
gravity,  which  is  the  ratio  between  the  weight  of  a  unit  volume 
of  water-Tree  soil  and  the  same  volume  of  water.  The  expression, 
volume  weight,  is  sometimes  applied  to  this  and  represents  the 
weight  of  a  unit  volume  of  soil.  The  apparent  specific  gravity  is 
numerically  smaller  than  the  real  specific  gravity  because,  in  the 
latter,  the  pore  space  is  eliminated.  The  apparent  specific  gravity 
varies  directly  as  the  kind  and  amount  of  minerals  and  the  com- 
pactness, and  inversely  as  the  amount  of  organic  matter  present 
and  the  porosity  of  the  soil.  Tt  is  obtained  by  dividing  the  weight 
of  a  certain  volume  of  soil  by  the  weight  of  the  same  volume  of 
water,  or.  what  amounts  to  the  same  thing,  the  weight  of  the  soil 
in  grams  by  the  volume  of  the  soil  in  cubic  centimeters. 

175 


176  SOIL  PHYSICS  AND  MANAGEMENT 

Under  different  systems  of  tillage  of  the  same  soil  type,  the 
apparent  specific  gravity  is  an  approximate  measure  of  the  tilth 
of  the  soil  when  determined  under  field  conditions.  In  order  to 
do  this  take  a  tube  with  a  cutting  edge  and  force  it  into  the  soil 
to  a  certain  depth  marked  on  the  tube,  thus  securing  a  definite 
volume  of  the  soil.  Dry,  weigh,  and  compare  with  an  equal  volume 
of  water,  or,  in  other  words,  determine  its  apparent  specific  gravity. 
The  soil  having  the  lowest  apparent  specific  gravity  is  in  best  tilth. 
As  an  illustration,  the  apparent  specific  gravity  of  brown  silt  loam 
from  a  heavily  cropped  field  was  1.36,  while  that  of  a  well  treated 
field  was  1.10,  indicating  that  the  latter  was  in  much  better  tilth 
than  the  former.  The  apparent  specific  gravity  of  soils  varies  from 
1.7,  that  of  sand,  to  0.5,  that  of  peat. 

3.  Weight  of  the  Soil. — The  weight  of  any  quantity  of  soil 
may  be  determined  by  multiplying  the  weight  of  an  equal  volume 
of  water  by  the  apparent  specific  gravity  of  the  soil.    A  cubic  foot 
of  soil  varies  from  106  pounds  to  31  pounds  per  cubic  foot,  the 
former  being  sand,  the  latter  peak     Knowing  the  weight  of  an 
acre-inch  of  water  to  be  226,000  pounds,  it  is  easy  to  obtain  the 
weight  of  an  acre-inch  or  any  number  of  acre-inches  of  soil.     (See 
the  table  page  120  for  weight  of  soil  strata.) 

4.  Color  of  Soils. — The  color  of  soils  is  one  of  the  most  notice- 
able or  striking  characteristics   and   always  appeals  to  practical 
farmers  as  one  of  the  best  means  for  indicating  soil  differences. 
Its  importance  in  estimating  the  character  of  the  soil  must  depend 
upon  the  material  producing  it.     Color  is  due  almost  entirely  to 
the  presence  of  two  substances,  organic  matter  and  iron  in  some 
form. 

The  color  imparted  by  organic  matter  varies  with  the  'amount 
present,  the  stage  of  its  humification,  the  moisture  content  of  the 
soil,  and  the  amount  of  limestone  present.  The  color  imparted 
varies  from  black  through  brown  to  gray.  The  least  decomposed 
imparts  a  brownish  color,  while  the  organic  matter  that  is  thor- 
oughly humified  gives  a  very  dark  brown  or  black  color  to  the  soil. 

The  presence  of  limestone  imparts  a  darker  color  to  the  organic 
matter  and  hence  to  the  soil.  It  further  aids  by  preventing  the 
leaching  out  of  the  black  humus  by  forming  insoluble  compounds 
with  it.  Soils  fairly  well  drained  but  deficient  in  limestone  are 
usually  light  in  color.  The  acid  of  soils  bleaches  the  organic  matter 
so  that  its  effect  in  coloring  soils  is  not  so  striking  as  in  those 
containing  limestone.  In  areas  of  acid  soils,  the  presence  of  lime- 


PHYSICAL  PROPERTIES  OF  SOILS  177 

stone  outcrops  are  indicated  by  dark  soils.  Coifey 1  speaks  of  being 
able  to  trace  an  outcropping  limestone  stratum  by  the  dark  color 
of  the  soil,  and  the  same  tiling  has  been  observed  in  the  southern 
part  of  Illinois  in  the  acid  soils  of  that  region.  In  soils  of  arid 
regions  limestone  is  frequently  so  abundant  as  to  impart  a  light 
color. 

Iron  oxides  give  various  colors  to  the  soil,  depending  upon  the 
degree  of  oxidation.  Ferric  oxide  (Fe.,0.,)  imparts  a  bright  reddish 
color.  Due  to  the  presence  of  this  oxide,  many  of  the  subsoils  of  the 
Piedmont  Plateau  are  decidedly  red  in  color.  Tbe  hydrated  ferric 
oxide  (2Fe.,03.;3H..())  imparts  a  dull  yellowish  color  to  the  soil,  but 
is  'sometimes  mixed  with  the  anhydrous  ferric  oxide,  giving  a  red- 
dish yellow  or  yellowish  red  color,  depending  upon  which  predomi- 
nates. In  some  cases,  deoxidation  has  occurred  through  the  effect 
of  organic  acids,  or  some  other  agency,  and  the  higher  oxides  of 
iron  have  been  reduced  to  the  lower  form.  This  gives  a  bluish, 
grayish  or  drab  color  to  the  soil.  This  is  especially  true  in  acid 
soils,  in  poorly  drained  ones,  and  in  subsoils  beneath  peat,  peaty 
loam  or  muck.  In  the  latter  case  the  iron  has  been  deoxidized  so 
completely  that  the  soil  usually  presents  a  uniformly  light  drab 
color.  The  most  striking  effect  of  deoxidation  is  seen  in  the  acid 
soils  where  drainage  is  intercepted  by  an  impervious  clay  stratum. 
The  iron  is  so  completely  deoxidized  that  the  subsurface  stratum 
is  frequently  white. 

Soil  constituents  themselves  in  some  cases  may  impart  color 
to  the  soil,  as  where  an  abundance  of  quartz  sand  is  found,  giving 
the  soil  a  grayish  or  whitish  cast.  Sometimes  mica  is  sufficient! v 
abundant  to  produce  a  glittering  appearance  in  the  soil.  In  sonic 
parts  of  the  Piedmont  Plateau  the  mica  formerly  existed  in  granitic 
rocks  in  large  crystals  from  one-half  to  one  and  one-half  inches  in 
diameter.  When  the  rock  decomposed,  the  mica  remained  as  large 
flakes,  giving  the  soil  a  glittering  appearance.  The  color  of  soils 
may  undergo  some  change,  usually  due  to  the  loss  of  organic  matter 
through  cropping,  but  mostly  because  of  erosion,  producing  yel- 
lowish brown  or  yellow  color. 

5.  Odor  of  Soils. — As  a  general  rule  soils  possess  a  distinct  but 
feeble  odor,  due  to  a  very  small  amount  of  an  organic  compound  of 
the  aromatic  family  and  analogous  to  that  of  the  camphorated 
bodies.  A  very  minute  quantity  is  present,  there  being  only  a  few 
millionth*  ~  of  a  per  cent. 
12 


178 


SOIL  PHYSICS  AND  MANAGEMENT 


6.  Number  of  Particles. — From  the  work  preceding,  especially 
the  tables  giving  the  diil'erent  grades  of  soil  material,  it  will  be 
seen  that  many  soil  particles  are  extremely  small,  and  the  number 
of  these  in  a  certain  volume  or  weight  of  soil  is  very  great.  If  the 
largest  particles  of  clay,  0.001  millimeter  in  diameter,  were  spherical 
and  could  be  arranged  in  columnar  form  in  a  cubical  box  one  inch 
each  way,  it  would  contain  15,625,000,000,000  particles.  The  de- 
termination of  the  number  of  particles  in  a  definite  weight  of  soil 
can  be  made  by  dividing  the  weight  of  soil  by  the  weight  of  a 
single  average-sized  particle,  as  given  in  the  following  formula : 
,,  _  Weight  of  soil  (grams) 
Weight  of  a  single  particle 

Weight  of  one  particle  =%7rD3  X  Sp.  gr. 

N  =  the  number  of  particles,  D  =  the  mean  diameter  of  the  soil  particle 
in  centimeters  and  ^D3  =  the  volume  of  a  sphere.  The  specific  gravity 
taken  is  2.65. 

This,  of  course,  assumes  that  the  soil  particles  are  spheres  and 
are  all  reduced  to  the  average  diameter.  The  following  table  gives 
the  number  of  soil  particles  per  gram  of  soil : 

Number  of  Particles  and  Internal  Surface  of  Soil  Separates 
Bureau  of  soils  groups 


Soil  separates 

Diameter,  mm. 

Number  of  particles 
in  one  gram 

Surface 
area  per 
gram, 
sq.  cm. 

Internal 
surface 
one  pound 
sq.  ft. 

Fine  gravel  

2.000  -1.000 

213 

15.1 

7.3 

Coarse  sand  

1.000  -0.500 

1,709 

30.2 

14.7 

Medium  sand  

0.500  -0.250 

13,668 

60.4 

29.5 

Pine  sand            .    ... 

0.250  -0.100 

134,480 

129.3 

63.1 

Very  fine  sand  

0.100  -0.050 

1,709,400 

302.1 

147.5 

Silt  

0.050  -0.005 

34,722,000 

824.8 

402.7 

Clay    

0.005  -0.0001 

46,296,296,000 

9,090.2 

4,439.4 

Illinois  experiment  station  groups 


Coarse  sand     

1.000  -0.320 

2,506 

34.3 

16.7 

Medium  sand  

0.320  -0.100 

77,821 

107.8 

52.6 

Fine  sand        

0.100  -0.032 

2,506,265 

343.0 

167.5 

Coarse  silt  

0.032  -0.010 

77,821,000 

1,078.2 

526.6 

Medium  silt  

0.010  -0.0032 

2,506,265,000 

3,429.8 

1,675.0 

Fine  silt          

0.0032-0.0010 

77,821,000,000 

10,781.6 

5,266.4 

Clay  

0.0010-0.00001 

5,596,597,275,000 

44,834.8 

21,896.1 

8.  Shape  of  Particles. — Particles  of  many  shapes  and  sizes 
exist  an  all  soils.  The  shape  varies  with  the  origin.  Soils  formed 
from  volcanic  ash  or  dust  are  most  irregular  in  shape  and  those  of 
wind  origin  are  more  nearly  uniform.  The  former  have  many 


PHYSICAL  PROPERTIES  OF  SOILS 


179 


elongated  or  lath-like  particles,  while  those  of  wind  origin  are 
generally  rounded.  Figure  87  gives  some  of  these  differences,  both 
as  to  shape  and  size.  The  closeness  of  packing  varies  with  the  shape 
of  the  soil  grains.  As  a  general  rule,  the  more  uniform  the  size 
and  shape  the  closer  the  packing  under  normal  conditions. 


Fio.  87. — (After  Merrill.)  A.  Showing  annular  character  of  quartz  psxrtirles  in  decom- 
posed gneiss.  B.  Quartz  granules  from  beach  sand.  C.  Showing  outlines  of  shreds  of  vol- 
canir  dust  art  Keen  under  the  microscope.  Hocks,  Hock-Weathering  and  Soila,  Merrill 
(Courtesy  Mafmillaa  Co.) 

9.  Arrangement  of  Particles. — There  is  no  definite  arrange- 
ment of  particles  in  soil's.  Coarse  sands  approacli  more  nearly  uni- 
formity than  any  others.  Theoretically,  there  are  two  general  form? 
of  packing  or  arrangement,  the  columnar,  figure  8.8  A.  and  oblique, 
figure  88B.  If  the  soil  particles  were  spheres  and  of  uniform  size, 
the  columnar  arrangement  would  give  47.64  per  cent  of  air  space, 


180 


SOIL  PHYSICS  AND  MANAGEMENT 


while  the  oblique  form  would  give  25.95  per  cent.  The  air  space 
with  columnar  arrangement  may  be  calculated  very  easily  by  taking 
a  one-inch  cubical  box  and  filling  it  with  marbles  of  different  sizes, 
varying  from  one  inch  to  one-sixteenth  inch  in  diameter,  and  coni- 

c 


FIQ.  87. 

puting  the  per  cent  of  air  space  left  in  the  box.  The  same  calcula- 
tion may  be  made  for  the  oblique  arrangement,  although  it  is  much 
more  difficult  because  of  the  mathematics  involved. 

If  instead  of  having  solid  particles,  as  in  figures  88A  and  B, 
A  B  c 


Fn.  88. — Diagram  showing  the  arrangement  of  soil  particles.     A,  columnar  or  vertical; 
B,  oblique;  C,  compound  granules. 

each  of  these  should  be  a  compound  granule  (Fig.  880)  made  up 
of  many  spherical  particles  with  the  same  arrangement  as  the  larger 
particles,  the  air  space  or  porosity  would  be.  for  columnar  arrange- 
ment, (47.64  per  cent  +  47.64  per  cent  of  52.36  per  cent)=  72.5ft 
per  cent,  or,  for  oblique  arrangement  (25.95  per  cent  +  25.95  per 


PHYSICAL  PROPERTIES  OF  SOILS 


181 


cent  of  74.05  per  cent)  ==45.17  per  cent.  The  latter  pore  space, 
45.17  per  cent,  is  approximately  that  possessed  by  the  medium  and 
fine  sandy  loams;  while  the  former,  72. 58  per  cent,  is  too  high  for 
soils  unless  under  exceptional  conditions.  The  coarse  sands  which 
approach  to  theoretical  conditions  most  nearly  show  33  to  35  per 
cent  of  pore  space.  The  granular  condition  developed  in  a  soil  in- 
creases its  pore  space. 

10.  Internal  Area  or  Surface. — The  total  surface  of  the  soil 
particles  in  a  given  volume  or  weight  is  called  the  internal  area  or 
•surface  of  the  soil,  and  is  usually  expressed  in  square  feet,  or  acres 
per  cubic  foot.  This  is  very  important  because  it  controls  to  a 
large  extent  the  amount  of  hygroscopic  and  capillary  or  film 
moisture.  A  system  of  grades  of  soil  particles  based  on  the  internal 
surface  would  be  of  great  value.  Since  the  surfaces  of  spheres 
vary  as  the  squares  of  their  radii  or  diameters,  the  internal  surface 
of  a  soil  varies  inversely  as  these  functions.  This  may  lie  shown 
by  means  of  marbles  as  above  and  calculating  the  total  surface 
with  each  diameter  for  columnar  arrangement. 

Area  of  Spheres  in  a  One-inch  Cubical  Box  with  Columnar  Arrangement 


Diameter  of  spheres 

Number  of  spheres  in  one 
cubic  inch 

Total  surface,  square  inches 

1  inch 

1 

3.1416 

y<i  inch 

8 

6.2832 

%  inch 

64 

12.5664 

1/8  inch 

512 

25.1128 

1/16  inch 

4,096 

50.2256 

1/1000  inch 

1,000,000 

3,141.16 

The  following  table  gives  the  internal  area  of  various  soils: 
Computed  Surfaces  of  Soil  Particles  in  Different  Kinds  of  Soil  King  s 


Kind  of  noil 

Effective 
diameter  of 
soil  grains 

Pore  space 

.Surface  of 
soil  grains  in 
one  cubic  foot 

Area  per 
cubic  foot 

Finest  clay  soil  
Fine  clay  soil  

mm. 

.004956 
.007657 

pt  r  cent 

52.94 
45.69 

square  feet 

173,700 
129,100 

acret 
3.98 

2.96 

Fine  clay  soil  

.008612 

48.00 

110,500 

2.56 

Heavy  red  clay  soil  
Loamy  clav  soil  

.01111 
.02542 

44.15 
49.19 

91,960 
70,500 

2.11 
1.64 

Clayey  loam.  .'. 

.01810 

47.10 

53.490 

1  .23 

Loam  

.02197 

44.15 

46,510 

1.06 

Loam  

.02619 

34.49 

45,760 

1  .05 

Sandy  loam  

.03035 

38.83 

36,880 

.84 

Sandy  soil  

.07555 

34.45 

15.S70 

.36 

Sandy  soil  

.1119 

32.49 

11,030 

.25 

Coarse  sandy  soil  

.1432 

34.91 

8,318 

.19 

182  SOIL  PHYSICS  AND  MANAGEMENT 

From  the  preceding  table  it  will  be  seen  that  the  total  surface 
area  of  the  particles  of  a  cubic  foot  of  very  fine  soil  is  about  four 
acres,  while  a  clayey  loam  contains  an  area  of  1.23  acres  per  cubic  foot 
and  a  coarse  sandy  soil  about  one-fifth  of  an  acre.  Careful  calcula- 
tions show  that  a  silt  loam  contains  from  05,000  to  75,000  square  feet 
per  cubic  foot.  Taking  a  soil  with  an  internal  surface  of  70,000 
square  feet  per  cubic  foot,  the  area  of  the  particles  in  an  acre  to  a 
depth  of  one  foot  would  be  about  109  square  miles,  or  three  town- 
ships. To  a  depth  of  four  feet,  from  which  plants  take  most  of 
their  moisture,  the  total  area  of  the  soil  particles  in  the  silt  loams 
is  not  far  from  436  square  miles  per  acre,  or  twelve  townships. 
The  capillary  water  is  distributed  over  this  surface.  If  the  roots  of 
a  corn  plant  did  not  pass  beyond  the  middle  of  the  rows,  and  no 
more  than  four  feet  deep,  each  hill  would  have  approximately  51.3 
acres  of  soil  particle  surface  from  which  to  draw  its  supply  of 
moisture  and  food. 

The  following  table  shows  the  variations  in  the  internal  surface 
of  some  of  the  common  soil  types  in  the  loessial  areas  of  the  middle 
west: 

Internal  Area  of  Soil  Types,  Calculated  from  Their  Physical  Composition 4 


Soils 

Internal  area  per  cubic  foot 

Dune  sand  

square  feet 

30,310 
55,380 
69,780 
70,900 
81,780 
136.700 

acres 

.696 
1.271 
1.602 
1.628 

1.877 
3.138 

Brown  sandy  loam      .         .            ... 

Yellow  gray  silt  loam  

Brown  silt  loam  

Black  clay  loam  

Drab  clav.  . 

11.  Porosity  of  Soils. — Porosity  is  the  total  amount  of  air 
space  in  soils  and  is  usually  expressed  in  per  cent  of  volume.  It 
depends  upon  the  relation  of  solid  particles  to  the  interstitial  space. 
This  is  modified  to  a  large  extent  by  the  size  and  shape  of  the  par- 
ticles, granulation,  tillage  and  amount  of  organic  matter.  Porosity 
or  total  pore  space  varies  inversely  as  the  size  of  the  soil  particles 
and  increases  with  their  irregularity  of  form.  For  this  reason 
volcanic  ash  soils  possess  great  porosity.  Granulation  and  good 
tilth  increase  the  porosity  of  soils,  and  puddling  diminishes  it. 
Tillage  exerts  a  favorable  influence  on  porosity,  but  sometimes  in- 
creases it  to  an  injurious  extent.  Porosity  varies  directly  as  the 
amount  of  organic  matter.  It  is  usually  lessened  by  the  rearrange- 


PHYSICAL  PROPERTIES  OF  SOILS  183 

ment  of  the  soil  particles  upon  wetting,  especially  in  soils  low  in 
organic  matter. 

The  porosity  may  be  determined  by  dividing  the  difference  be- 
tween the  real  and  the  apparent  specific  gravity  by  the  real,  or  by 
the  following  formula : 

Real  Sp,  gr.  —  App.  Sp.  gr. 
Porosity  =  -  ^  . -    - 

Real  Sp.  gr. 

The  porosity  of  different  grades  of  sand  has  been  determined 
in  this  way  and  the  results  are  given  in  the  following  table : 

Porosity  of  Different  Grcules  of  Sand  4 


Loose 

Compact 

1. 

Passes  a  sieve  20  meshes  to  the  inch;  held  by  a 
40-mesh    

per  cent 

40.04 

per  cent 

36.83 

?, 

Passes  40-mcsh;  held  by  60-mesh 

42.07 

37.69 

3 

Passes  60-mesh;  held  by  8()-inesh 

44.64 

39.62 

4 

Passes  80-mesh;  held  by  100-inesh  

45.92 

41.39 

5. 

Passes  100-niesh.     It  contains  all  of  the   fine 
particles  

46.00 

40.49 

The  porosity  of  the  soil  under  field  conditions  is  of  much  more 
importance  than  that  of  the  laboratory  sample,  after  having  been 
finely  ground.  The  laboratory  determination  gives  comparative  re- 
sults, however,  that  are  of  some  value.  The  porosity  may  best  be 
obtained  by  taking  the  apparent  specific  gravity  under  field  con- 
ditions, a.s  given  on  page  IT."),  and  the  real  specific  gravity  of  tin- 
soil  and  use  these  in  the  formula  above.  Soils  in  good  tilth  have 
high  porosity.  It  is  not  unusual  for  the  same  type  of  soil  from 
different  fields  to  have  a  difference  of  10  per  cent  or  even  more 
of  pore  space  in  favor  of  the  soil  of  good  tilth.  The  total  pm- 
space  varies  inversely,  while  the  si/e  of  the  individual  pores  varies 
directly  as  the  size  of  the  particles.  The  total  pore  space  of  coarse 
soils  as  sands  is  small  but  the  pores  are  large.  The  sectional  areas 
of  individual  pores  vary  as  the  squares  of  the  diameter  of  the  soil 
particles.  In  figure  SSA  there  are  1(5  pores  per -square  inch,  while 
if  the  particles  are  one-half  as  large  they  number  <H.  The  sectional 
area  can  be  only  one-fourth  as  large  in  the  latter  case  as  in  the 
former.  If  coarse  sand  whose  particles  have  a  diameter  of  one- 
twenty-fifth  of  an  inch  is  compared  with  clav  whose  particles  are 
one  twenty-five-thousandth  of  an  inch  it  will  be  S<HMI  that  for  sand 


184 


SOIL  PHYSICS  AND  MANAGEMENT 


with  columnar  arrangement  there  will  be  625  pores  per  square  inch 
and  with  clay  625,000,000.  The  former  will  be  one  million  times 
as  large  as  the  latter.  The  large  size  of  the  pores  permits  certain 
physical  processes,  such  as  percolation  and  aeration,  to  take  place 
so  readily  that  they  may  be  detrimental  to  the  crop.  On  the  other 
hand,  fine-grained  soils,  as  clays  and  clay  loams,  with  their  very 
minute  pores,  but  large  total  pore  space,  may  so  retard  percolation 
and  aeration  as  to  be  equally  detrimental  to  the  crop.  Medium- 
grained  soils,  as  silt  loamls  or  fine  sandy  loams  possessing  an  inter- 
mediate pore  space,  fere  best  suited  to  most  crops,  although  both  the 
coarse  and  very  fine  soils  have  their  advantages  under  certain  con- 
ditions. The  size  of  the  pores  in  fine-grained  soils  is  increased  by 
granulation. 

The  following  table  shows  the  porosity  of  different  types  of  soils : 

Porosity  in  Soils  of  Varied  Physical  Composition  * 


Organic- 
matter  content 

Loose 

Compact 

Sand  

per  cent 

0.75 

per  cent 

44.9 

per  cent 

39.7 

Brown  sandy  loam  (medium  sand)  .  . 
Yellow  fine  sandy  loam  (loess)   .... 

2.90 
0.80 

53.7 
59.0 

43.3 
49.9 

White  silt  loam 

0.79 

59.7 

50.2 

Brown  silt  loam  

4.88 

60.4 

50.4 

Black  clay  loam  

5.50 

61.2 

52.7 

Drab  clay          ...               .    . 

3.60 

68.2 

58.2 

Peat  

64.48 

65.6 

60.8 

The  total  pore  space  of  soils  is  rarely  less  than  30  per  cent. 
Coarse,  clean  sand  has  about  this  amount.  This  means  that  a  cubic 
foot  of  such  soil  will  contain  70  per  cent  of  solid  material.  In  case 
of  sandy  loams  and  silt  loams,  the  pore  space  amounts  to  about  50 
per  cent,  or  half  of  the  volume  of  the  soil,  or,  in  a  cubic  foot,  there 
are  approximately  862  cubic  inches  of  air  space.  The  increase  in 
porosity,  within  certain  limits,  is  beneficial  because  of  the  increase 
in  aeration.  Extremely  large  air  spaces  in  soils  are  detrimental 
because  they  permit  of  excessive  evaporation. 

QUESTIONS 

1.  What  is  specific  gravity? 

2.  Give  specific  gravity  of  a  few  common  soil-forming  minerals. 

3.  What   is  the   apparent  specific  gravity? 

4.  How  is  it  determined? 

5.  How  does  porosity  affect  it?     Tilth? 

6.  How  is  the  weight  of  a  cubic  foot  of  soil  determined? 


PHYSICAL  PROPERTIES  OF  SOILS  185 

7.  If  a  soil  has  an  apparent  specific;  gravity  of  1.4,  what  is  the  weight  of 

the  surface  soil  per  acre? 

8.  Why  is  color  of  soils  so  important? 

9.  What  color  is  imparted  by  organic  matter? 

10.  What  effect  does  limestone  have  on  color? 

11.  What  colors  are  due  to  iron? 

12.  Why  are  subsoils  in  swamps  so  frequently  gray  or  drab? 

13.  The  subsoil  above  the  tight  clay  stratum  is  usually  gray  in  color.     Why 

is  this? 

14.  What  is  peculiar  of  the  subsoils  of  the  Piedmont  Plateau? 

15.  What  soil  constituents  impart  color? 

1(5.  Explain  how  soils  may  undergo  change  in  color. 

17.  What  can  be  said  of  the  odor  of  soils? 

18.  If  soil  particles  average  0.02  inch  in  diameter,  how  many  could  be  placed 

in  a  one-inch  cubical  box  with  columnar  arrangement?     If  0.02  mm.? 

19.  How  many  particles  in  a  gram  of  soil  if  the  particles  average  0.005  mm. 

in  diameter? 

20.  Upon  what  does  the  shape  of  the  particles  depend? 

21.  What  property  does  this  affect? 

22.  Define  internal  surface  of  a  soil. 

23.  How  does  the  internal  surface  vary? 

24.  How  do  the  areas  of  spheres  vary  ? 

25.  If  a  cubic  foot  of  soil  has  an  internal  surface  of  50,000  square  feet  and 

it  contains   20.8   pounds   of  moisture,  how  thick    would   the   film  of 
water  be  if  uniformly  distributed  over  the  surface? 

26.  What  is  the  internal   surface  in  acres  of  an  acre  of  coarse  sandy  soil 

4  feet  deep  ?     ( Table  page  181.) 

27.  Of  an  acre  of  the  clay  soil  as  given  in  the  table  on  page  182? 

28.  What  two  arrangements  for  soil  particles? 

29.  If  a  two-inch  cubical  box  is  filled  with   shot  one-sixteenth  of  an  inch 

in  diameter  arranged  in  columnar  form,  how  many  will  it  hold? 

30.  What  per  cent  of  air  space  will  remain? 

31.  How  is  the  porosity  modified? 

32.  What  effect  does  wetting  have  on  total  pore  space? 

33.  How  is  porosity  of  a  soil  determined? 

34.  How  is  the  porosity  of  a  soil  under  field  conditions  determined? 

35.  What  relation  betwen  the  total  pore  space  and  the  si/e  of  the  pores? 
30.  If  soil  particles  are  one-thousandth  of  an   inch    in   diameter,   spherical 

and  arranged   vertically   in  a   one-inch   cube,   what  will   lie  the  total 
sectional  area  of  the  pores?     Of  a  single  pore? 

37.  In  the  table  on  page   183  why  is  the  porosity  of  the  compact  in  .">  less 
than  in  4? 

REFERENCES 

Toffey,  O.  X.,  Hull.  85.  Bureau  of  Soils,  p.  42. 

'Wilev,  II.  W.,  The  Principles  and  Practice  of  Agricultural  Analyses,  100(i, 

p!  94. 
'King,  F.  II.,  Physics  of  Agriculture,  Mrs.  F.  H.  King,  Madison.  Wis.,  1901, 

p.  124. 
*  Unpublished  data  Soil   Physics  Division,  University  of  Illinois. 


CHAPTER   XIV 
WATER  OF  SOILS 

PLANT  growth  cannot  take  place  without  moisture.  Plants  con- 
sist of  from  60  to  over  90  per  cent  of  water.  This  represents  only 
a  very  small  part  of  the  water  used,  since  many  plants  transpire  in 
twenty-four  hours  an  amount  equal  to  their  weight.  Water  is  of 
primary  importance  in  many  physical  and  all  chemical  changes 
that  take  place  in  the  soil. 

Some  Physical  Characteristics  of  Water. — Water  has  certain 
physical  characteristics  that  should  be  noted  here.  Its  volume 
changes  with  temperature.  Its  maximum  density  is  attained  at  4 
degrees  C.,  39.2  F.,  and  expansion  takes  place  either  above  or  below 
this  temperature,  and  at  15  degrees  C.,  59  F.,  the  density  as  com- 
pared with  water  at  4  degrees  C.  is  0.99.  At  the  freezing  point  the 
density  of  water  is  0.99988,  while  the  density  of  ice  at  the  .same 
temperature  is  0.928.  In  the  melting  of  ice  a  large  amount  of  heat 
is  used,  but  it  does  not  raise  the  temperature.  This  heat  becomes 
latent  or  is  used  in  changing  the  condition  of  the  water  from  a 
solid  to  a  liquid.  It  requires  more  heat  to  melt  (fuse)  ice  than  to 
fuse  metals.  To  melt  one  gram  of  ice  requires  80  calories,*  whereas 
metals  require  from  5  to  77  calories.  Expressed  in  Fahrenheit- 
pounds,  the  English  system,  the  figures  are  144  for  ice  and  from 
9  to  138.6  heat  units  for  metals. 

In  the  evaporation  of  water  a  similar  phenomenon  is  observed. 
When  the  boiling  point  is  reached  no  further  change  in  temperature 
of  water  occurs,  but  the  heat  is  used  in  changing  the  water  from 
a  liquid  to  a  gas.  To  effect  this  change  in  one  gram  537  calories 
are  necessary,  or,  with  the  Fahrenheit-pound,  966.6  heat  units.  It 
must  be  remembered  that  when  water  evaporates,  an  amount  of 
heat  equivalent  to  the  above  is  used,  regardless  of  the  temperature. 
In  changing  from  a  higher  to  a  lower  temperature,  or  from  gaseous 
to  liquid  form,  or  from  liquid  to  solid,  equivalent  amounts  of  heat 
are  liberated. 

*  A  calorie,  in  general,  is  the  amount  of  heat  required  to  raise  the  tem- 
perature of  a  gram  of  water  one  degree  centigrade.    A  heat  unit  or  a  British 
thermal  unit  is  the  heat  required  to  raise  one  pound  of  water  one  degree 
Fahrenheit. 
186 


WATER  OF  SOILS  187 

Specific  Heat. — The  amount  of  heat  required  to  raise  one  unit 
mass  of  a  substance  one  degree  in  temperature  as  compared  to  that 
of  the  same  weight  of  water  is  the  specific  heat  of  a  substance.  The 
specific  heat  of  water  exceeds  that  of  every  other  substance  and  is 
used  as  the  standard  or  1.0.  Substances  with  low  specific  heat 
change  temperature  rapidly. 

Viscosity. — The  fluidity  or  viscosity  of  water  varies  with  tem- 
perature and  with  substances  in  solution.  If  at  0  degrees  C.,  the 
viscosity  is  100;  at  50  degrees  C.  it  is  31. 

Some  substances  when  dissolved  in  water  increase  the  viscosity, 
while  others  decrease  it. 

Uses  of  Water. — Green  plants  contain  a  very  large  percentage 
of  water,  as  stated  above.  A  constant  stream  is  passing  in  through 
the  roots  and  transpired  by  the  leaves.  From  300  to  500  pounds 
of  water  are  required  for  every  pound  of  dry  matter  of  the  plant. 
The  soil  then  must  contain  a  sullicient  amount  and  must  be  of 
such  character  that  it  can  deliver  to  the  plant  this  enormous  amount. 
If  this  is  not  supplied,  the  plant  is  stunted  or  may  wilt  and  die 
before  maturity.  The  uses  of  water  in  soils  are  as  follows : 

(1)  Directly  as  a  plant  food,  taking  part  in  the  building  up 
of  tissues,  either  as  water  or  indirectly  by  being  used  in  combina- 
tion with  other  elements. 

(2)  As  a  solvent  for  various  substances  in  the  soil  that  may  be 
used  by  plants.     It  was  believed  by  Jethro  Tull  that  plants  fed 
directly  upon  the  very  fine  soil  particles,  taking  them  in  through 
the  roots,  and  that  this  accounted  for  the  better  growth  of  crops  in 
well  pulverized  soils. 

(3)  As  a  means  by  which  those  nutrient  solutions  are  brought 
to  and  taken  into  the   plant,  either  along  with   the  water  or  by 
diffusion. 

(1)   As  a  regulator  of  certain  physical  phenomena. 

(5)  As  an  aid  to  chemical  action  produced  directly  or  through 
the  agency  of  bacteria. 

The  Amount  of  Water  Required  by  Plants. — Experiments 
have  been  carried  on  in  various  parts  of  the  world  by  different 
investigators  to  determine  the  amount  of  water  used  in  producing  a 
crop.  More  or  less  transpiration  is  going  on  constantly  during 
growth,  and  an  enormous  amount  of  water  passes  out  through  the 
stomates  of  the  leaves.  Tbe  following  table  gives  the  amount  of 
water  required  to  produce  a  pound  of  dry  matter,  as  determined  by 
different  investigators. 


188 


SOIL  PHYSICS  AND  MANAGEMENT 


Water  Transpired  by  Growing  Plants  for  One  Part  of  Dry  Matter  Produced 


Lawes  and  Gilbert,1 
England 

Hellriegel,*  Germany 

Wollny.t  Germany 

King.t  Wisconsin 

Beans  

214 
225 
235 
249 
262 

Beans  (horse)  262 
Wheat  (spring)359 
Peas      292 

Maize  

233 
416 
447 
912 
774 
665 
646 
843 
490 

Corn  (maize)  271 
Potatoes.  ...  385 
Peas      .  .      477 

Wheat     .  .  . 

Millet  

Peas  
Red  clover.  .  . 
Barley  

Peas.... 

Red  clover....  330 
Barley  310 

Rape..   . 

Red  clover  .  577 
Barley  464 
Oats                504 

Barley  .... 

Oats      .    .       402 

Oats 

Buckwheat..  371 
Lupine  373 

Buckwheat  . 
Mustard  .  .  . 
Sunflower  .  . 

Rye  (spring).  377 

Average.  .  .  . 

237 

Average  .  .  .  342 

Average  .  . 

.  603 

Average  .  .  446 

*  Hellriegel*  used  quartz  sand  in  small  amounts  and  supplied  the  necessary  plant  food 
in  solution.  Figures  include  some  loss  of  water  by  evaporation,  which  was  not  prevented 
at  first,  but  later  reduced  by  means  of  covers. 

t  Wollny'  used  small  quantities  of  sand  well  supplied  with  organic  matter.  Perforated 
covers  materially  reduced  evaporation;  this,  however,  was  checked  up  on  soil  growing  no  crop. 

I  King4  used  about  400  pounds  of  normal  soils,  in  cans,  some  set  down  in  the  earth.  Some 
were  run  in  the  field,  others  in  greenhouses.  Water  was  added  from  beneath,  so  that  evap- 
oration was  very  slight. 

We  see  from  the  above  table  that  the  water  required  to  pro- 
duce one  pound  of  dry  matter  varies  from  214  pounds  in  the  case  of 
beans,  as  determined  by  Lawes  and  Gilbert,  of  England,  to  912 
pounds  for  rape,  as  determined  by  Wollny,  of  Germany.  The  average 
of  all  determinations  shown  above  is  428  pounds.  King's  deter- 
minations in  Wisconsin  probably  apply  better  for  the  humid  sec- 
tion of  this  country  than  any  others  that  have  been  made.  The 
number  of  trials  made  by  King  was  as  follows :  Peas,  1 ;  barley, 
5;  potatoes,  14;  oats,  20;  clover,  46,  and  corn  (maize),  52.  With 
the  water  requirements  as  determined  by  King,  a  100-bushel  crop 
of  corn  would  require  approximately  16  inches  of  water  to  produce 
it,  or  18  tons  per  bushel  of  grain ;  a  100-bushel  crop  of  oats,  about 
18*  inches,  or  20  tons  per  bushel ;  a  50-bushel  crop  of  wheat,  12.7 
inches,  or  28.7  tons  per  bushel,  and  a  four-ton  crop  of  clover,  20 
inches  of  water. 

Briggs  and  Shantz  have  made  determinations  of  water  require- 
-  ments  of  plants  in  the  arid  regions  of  the  United  States,  and  their 
results  are  given  in  the  table,  page  242. 

Dependent  Upon  Transpiration.  -  The  amount  of  water 
required  by  plants  is  dependent  upon  the  amount  of  transpiration, 
which  in  turn  depends  upon  several  factors,  as  follows : 

(1)  High  temperatures  increase  and  low  temperatures  retard 
transpiration. 

(2)  Movement  of  the  air  increases  transpiration  from  the  plant, 


WATER  OF  SOILS  189 

while  the  movement  of  the  plant  itself  aids  the  circulation  of  the 
water  within  the  plant,  and  so  increases  transpiration. 

(3)  Low  humiditv  is  favorable  to  transpiration. 

(4)  The  character  of  the  soil  is  an  important  factor.     More 
transpiration  takes  place  from  plants  on  poor  soils  than  on  those 
well  supplied  with  plant  food. 

(o)  Transpiration  increases  with  the  brightness  of  the 
sunshine. 

(0)  The  more  moisture  there  is  in  the  soil  the  greater  is  the 
transpiration. 

The  Supply  of  Moisture  in  Soils. —  1.  Rainfall. — The  supply 
of  moisture  in  soils  depends  primarily  on  the  rainfall.  The  excep- 
tions are  where  artificial  irrigation  is  practiced  or  where  water  is 
brought  to  a  region  through  some  porous  substratum  and  then 
reaches  the  surface  by  hydrostatic  pressure.  The  following  table 
shows  the  annual  precipitation  for  different  portions  of  the  earth's 
surface : 

Precipitation  on  Earth's  Surface  5 


Annual  precipitation  PerreutaRo  of  earth1 

land  surf  arc- 


Under  10  inches 25.0 

From  10  to  20  inches 30.0 

From  20  to  40  inches 20.0 

From  40  to  60  inches 1 1 .0 

From  b'O  to  80  inches 9.0 

From  80  to  120  inches 4.0 

From  120  to  160  inches. .  0.5 


Above  160  inches 


0.5 


100.0 


It  is  seen  from  the  table  that  r>o  per  cent  of  the  land  area 
receives  less  than  *^0  inches  of  rainfall  annually,  while  only  5  pel- 
cent  receives  over  SO  inches.  In  the  I'nited  States  fully  50  per  cent 
of  the  total  area  receives  less  than  ^o  inches  of  rainfall,  and  over  a 
very  large  part  of  this  the  growing  of  crops  is  practicallv  impossible 
except  under  irrigation.  (Sec  Rainfall  Map,  Fig.  S!>. )  In  almost 
all  regions  whero  crops  depend  upon  rainfall,  its  unequal  distribu- 
tion, or  the  frequent  recurrence  of  periods  of  drouth,  results  in 
reduced  yields. 

In  almost  every  season  in  some  parts  of  even  so  small  an  area 
as  a  single  State  crops  are  injured  to  a  greater  or  less  extent  by 
drouth.  In  some  cases  the  dry  weather  occurs  early  in  the  spring. 


190 


SOIL  PHYSICS  AND  MANAGEMENT 


WATER  OF  SOILS  191 

in  April  or  May,  but  it  occurs  more  often  in  July  or  August,  at  the 
time  when  the  growing  crops  are  in  greatest  need  of  moisture.  At 
the  University  of  Illinois'1  the  distribution  of  rainfall  is  so  irregular 
that  in  the  past  twenty-five  years  seven  Aprils  have  been  dry  or 
have  had  less  than  two  inches  of  rainfall,  and  during  this  same 
time  four  Mays,  eight  Junes,  five  Julys,  six  Augusts,  and  eleven 
Septembers  have  been  dry,  or  a  total  of  41  out  of  150  growing 
months  for  the  25  years.  In  the  southern  third  of  the  State  the 
distribution  is  still  more  irregular,  and  drouth  is  more  injurious 
there,  because  of  the  greater  evaporation  and  the  character  of  the 
soil.  This  illustrates  quite  well  the  conditions  generally  in  the 
humid  area. 

2.  Soil. — The  supply  of  moisture  for  the  crop  depends  upon 
the  character  of  the  soil  itself.     An  open  porous  soil,  such  as  a 
coarse  sandy  loam  or  sand,  will  lose  a  great  deal  of  moisture  by  per- 
colation, and  hence  will  not  have  a  large  supply  for  crops.     Fre- 
quent rains  are  necessary  for  'such  a  soil.     However,  the  "firing" 
of  the  crop  on  sandy  soil   is  not  always  an  indication  of  lack  of 
moisture.    On  finer  grained  soils,  however,  the  moisture  is  retained 
much  better  and  an  abundant  supply  is  usually  present  for  the 
growing  crop.     The  retentive  power  of  the  soil  is  increased  very 
materially  by  the  presence  of  organic  matter.     Probably  no  one 
constituent  plays  a  greater  part  in  maintaining  the  supply  of  moist- 
ure in  the  soil  than  that  of  organic  matter. 

3.  Loss  by  Evaporation. — In  a  soil  deficient  in  organic  mat- 
ter,  consisting  of  medium-sized   soil    particles,   the  movement   of 
moisture  to  the  surface  and  its  evaporation  may  reduce  the  supply 
sufficiently  to  injure  the  crop.    This  factor  is  of  especial  importance 
in  semi-arid  and  arid  sections.     (See  Chapter  18.)     Mulrhes,  good 
tilth,  and  a  fair  supply  of  organic  matter  reduce  evaporation  to  a 
large  extent. 

Ways  of  Expressing  Moisture  Content. — The  moisture  con- 
tent of  soils  has  been  expressed  in  a  number  of  different  ways,  some 
of  which  have  been  discontinued  because  of  their  impracticability. 
Some  of  the  methods  are  as  follows:  (a)  per  cent  based  on  weight 
of  soil;  (b)  in  cubic  inches  or  per  cent  of  volume,  and  (c)  in  acre 
inches. 

(a)  Per  Cent  of  Weight  of  Soil. — In  expressing  the  moisture 
content  in  per  cent  various  methods  have  been  used.  A  few  inves- 
tigators have  based  it  on  the  weight  of  the  wet  soil  as  taken  from 
the  field.  This  is  not  satisfactory,  because  the  base  varies  from  day 
to  day  as  the  moisture  content  changes.  In  some  cases  the  per  cent 


192  SOILS  PHYSICS  AND  MANAGEMENT 

has  been  based  on  the  air-dry  soil,  and  while  this  is  somewhat  better 
than  the  former,  yet  it  is  subject  to  the  same  objection,  since  the 
air-dry  soil  varies  with  the  temperature  and  humidity  of  the  air. 
Without  doubt  the  most  satisfactory  base  for  expressing  the  per  cent 
is  the  weight  of  water-free  soil  obtained  by  drying  in  an  oven  at 
100  to  110  degrees  C.  Hilgard  has  used  the  temperature  of  200, 
others  140  degrees  C.,  for  obtaining  the  water-free  soil,  but 
in  general  practice  a  temperature  of  100  degrees  C.  is  easier  to 
maintain  and  just  as  satisfactory.  Probably  none  of  these  is  the 
exact  point  at  which  all  of  the  hygroscopic  moisture  is  driven  off. 
The  thing  desired  is  a  uniform  standard. 

(b)  Cubic  Inches  or  Per  Cent  of  Volume. — Expressing  the 
water  content  in  cubic  inches  or  per  cent  of  volume  may  have  its 
advantage  in  case  of  certain  soils,  such  as  peats,  or  mucks,  which 
are  very  light,  or  sands  which  are  heavy.    A  peat  soil  with  50  per 
cent  of  moisture  may  contain  no  more  than  a  silt  loam  with  20  per 
cent.    A  cubic  foot  of  peat,  water-free,  weighs  about  30  pounds,  and 
50  per  cent  of  moisture  would  mean  15  pounds  per  cubic  foot,  while 
the  silt  loam,  weighing  75  pounds  per  cubic  foot  with  20  per  cent, 
would  have  the  same  amount.    Expressed  in  per  cent  of  volume,  the 
amount  would  be  24  in  each  case.     To  determine  the  per  cent  of 
volume  necessitates  the  finding  of  the  per  cent  of  moisture  based 
on  the  water-free  soil. 

(c)  Acre-inches. — It  is  often  desirable  to  express  the  water 
content  of  soils  for  convenient  comparison  with  the  rainfall.    This 
may  be  done  in  square-foot-inches  or  in  acre-inches,  the  depth  of 
water  in  inches  over  a  square  foot  or  an  acre.    To  do  this  it  is  neces- 
sary to  determine  the  weight  of  water  in  the  soil  per  square  foot  to 
the  depth  desired.    The  weight  of  water  in  a  cubic  foot  in  pounds 
divided  by  5.2,  the  weight  of  a  square-foot-inch  of  water,  will  give 
the  depth  in  inches. 

QUESTIONS 

1.  What  amount  of  water  is  required  by  plants? 

2.  Give  the  effects  of  temperature  changes  on  water. 

3.  What  is  latent  heat? 

4.  Give  comparison  of  metals  and  water  as  to  the  amount  of  heat  required 

to  change  the  condition  or  state. 

5.  Give  differences  between  the  calorie  and  English  heat  unit. 
f>.  Define  specific  heat. 

7.  How  does  water  compare  with  other  substances?  . 

8.  What  factors  modify  viscosity? 
0.  Give  uses  of  water  in  soils. 

10.  How  much  water  is  required  for  a  pound  of  dry  matter? 


WATER  OF  SOILS  193 

11.  How  much  for  a  50-bushel  corn  crop?     A  GO-bushel  oat  crop? 

12.  Upon  what  does  the  amount  of  water  used  by  plants  depend? 

13.  How  much  of  the  earth's  land  surface  is  adapted  to  ordinary  humid 

agriculture? 

14.  What  part  of  the  United  States  is  humid?     (See  Rainfall  Map,  Fig.  86.) 

15.  How  does  the  rainfall  vary  during  different  months? 
1(5.  How  does  soil  affect  the  moisture  supply? 

17.  What  part  does  evaporation  play  in  the  storage  of  water? 

18.  What   are  the   advantages   and   disadvantages   of   expressing   moisture 

content  in  per  cent  of  weight  of  soil? 

19.  What  is  the  best  base  to  use?     Why? 

20.  Give  advantages  of  expressing  moisture  content  in  cubic  inches  or  per 

cent  of  volume. 

21.  Why  is  it  well  to  express  the  moisture  content  in  acre-inches? 

REFERENCES 

1  Lawes  and  Gilbert,  Jour.  Hort.  Soc.,  18f>0. 

*Hellriegel,  Kxperiment  Station  Record.  IV,  p.  f>32. 

3  Wollny,  Experiment  Station  Record,  IV,  p.  532. 

«King,*F.  11.,  Physics  of  Agriculture,  1007,  p.  130,  also  llth  and  14th  An- 
nual Reports  Wisconsin  Station. 

•Widtsoe,  J.  A.,  Dry  Farming.  1911,  p.  33. 

'  Mosier,  J.  G.,  Bulletin  208,  Illinois  Experiment  Station,  Climate  of 
Illinois,  1917. 


13 


CHAPTER  XV. 

WATER  OF  SOILS 

I.   HYGROSCOPIC   MOISTURE 

WATER  is  held  in  soils  by  the  manifestation  of  attractive  force 
under  three  forms:  (1)  hygroscopic,  or  adhesion;  (2)  surface 
tension,  and  (3)  hydrostatic,  or  gravity.  These  give  rise  to  the 
three  so-called  forms  of  water — hygroscopic,  capillary,  or  film,  and 
gravitational.  '  It  must  be  remembered  that  the  water  of  all  is  the 
same  in  chemical  composition,  the  only  difference  being  in  the  force 
holding  or  moving  it  in  the  soil. 

Hygroscopic  Moisture. — All  substances  have  the  power  of  con- 
densing moisture  upon  their  surfaces,  hence  a  very  thin  film  of 
water  exists  around  all  substances  exposed  to  the  air.  This  phenom- 
enon is  known  as  adsorption.  The  water  is  held  very  firmly  by  ad- 
hesion or  molecular  force,  which  is  estimated  as  equal  to  10,000 
atmospheres,  and  the  water  may  be  removed  only  by  a  temperature 
much  higher  than  the  ordinary.  When  normal  temperature  is 
restored,  the  moisture  will  again  be  slowly  condensed  upon  the  sur- 
face. Briggs  1  has  calculated  the  thickness  of  the  hygroscopic  film 
for  quartz  particles  as  2.66  X  10~6  centimeters,  or  0.0000266  milli- 
meter. The  amount  of  hygroscopic  moisture  in  a  soil  depends  upon 
several  factors. 

Hygroscopic  Capacity  of  Soils  2 


Soil 

Amount 
of  clay 

Minimum 
moisture 

Maximum 
moisture 

Average 

Sandy  soils    

per  cent 

Less  than  5 

per  cent 

0.79 

per  cent 
4.18 

per  cent 
2.59 

Sandy  loams  

5  to  10 

1.84 

6.12 

3.39 

Loams  

10  to  15 

2.30 

9.18 

5.19 

Clay  loams  

15  to  20 

5.06 

10.26 

6.49 

Clays     

Over  20 

4.20 

18.60 

10.83 

(a)  Size  of  Particles. — The  amount  of  hygroscopic  moisture 
in  soils  varies  inversely  as  the  size  of  the  particles  and  directly  as 
the  internal  surface  of  the  soil.  Since  colloids  are  made  up  of  very 
minute  particles,  a  small  amount  present  will  increase  very  mate- 
rially the  internal  siirface  and  consequently  the  total  amount  of 
194 


HYGROSCOPIC  MOISTURE 


195 


tin's  form  of  moisture.  Sandy  soils  with  a  relatively  small  surface 
area  contain  only  small  amounts  of  hygroscopic  water. 

The  preceding  tahle  shows  the  amount  of  hygroscopic  moisture 
as  determined  hy  Hilgard.  The  soils  were  exposed  in  saturated 
atmosphere  at  15  degrees  C.  and  dried  at  200  degrees  (>. 

This  shows  the  effect  of  texture  and  consequently  the  internal 
surface  upon  the  amount  of  hygroscopic  moisture.  In  another  case 
the  hygroscopic  capacity  was  determined  for  the  whole  soil  and  then 
for  the  separates  as  follows : 

Per  cent 

Whole  soil 5.24 

Clay    1 7.1)0 

Hydraulic  Value  less  than  0.25  nun.  per  second.  .  .  .      7.00 

Hydraulic  Value  0.25  mm 2.01 

Hydraulic  Value  0.50  mm 1.7.3 

(h)  Colloids. — The  colloids  have  a  very  high  adsorptive  power 
for  water,  and  their  presence  in  soils  increases  very  strikingly  the 
hygroscopicity.  Nearly  all  soils,  and  more  particularly  the  heavy 
ones,  contain  considerable  amounts  of  colloids.  They  may  occur 
as  humus,  ferric  oxide,  silicic  acid,  or  hydrous  aluminum  silicates. 
Ilydrated  ferric  oxide  and  some  other  minerals  may  unite  with 
water  chemically,  but  the  common  hygroscopic  phenomenon  is  one 
of  adsorption.  This  table  shows  the  effect  of  colloids  on  the.  hygro- 
scopic moisture. 

Influence  of  Silt,   Sand,    Clay,    Ferric  Hydrate  and  Humus  on   Hygroscopic 

Capacity  3 


Missis- 
sippi 
pin<; 
hills 
snn<ly 
lonni 

Wash- 
ington 
dust 
soil 

Missis- 
sippi 
white 
pipe 
day 

Missis- 
sippi 
flat- 
woods 
clay 
soil 

Missis- 
sippi 
ferru- 
ginous 
clav 
s<il 

Oahu 
ferru- 
ginous 
laterite 

Missis- 
sippi 
marsh 
muck 

Missis- 
sippi 
marsh 
soil 

I  fygroscopic  moist  uro 
Clay 

2.48 
2.1)4 

4.92 
1.27 

9.09 
74.05 

9.33 
25.4S 

1S.OO 

2S  15 

19.60 

7 

21.00 
Tr 

15.40 
Tr 

Ferric  hvdnvte  

1.04 

.15 

12.10 

51.  (X) 

Humus     

.55 

.44 

0.00 

.50 

little 

3.33 

00  10 

19  S3 

Finest     silts     (0.01- 
0.0250  mm.) 

60.10 

-45.04 

23.15 

OX.OO 

40.33 

1 

33  94 

S  70 

Sands,  fine  and  me- 
dium   (0.0250-0.50 
mm  ) 

31.20 

42.40 

.20 

4  70 

1501 

J45.00 
1 

70  IS 

It  will  be  seen  from  the  above  table  that  clay,  ferric  hydrate  and 
humus  have  the  greatest  effect  upon  hygroscopic  capacitv. 

(c)  Temperature.  —  The  temperature  affects  the  amount  of 
hygroscopic  moisture,  since  under  temperatures  higher  than  normal 


196 


SOIL  PHYSICS  AND  MANAGEMENT 


a  part  of  the  hygroscopic  moisture  is  driven  off.  Condensation  will 
again  take  place  when  the  temperature  becomes  lower.  If,  however, 
the  air  is  saturated  with  moisture  an  increase  in  temperature 
increases  the  amount  of  moisture  adsorbed. 

Hilgard  has  found  that  a  fine  sandy  soil  that  adsorbed  two  per 
cent  of  moisture  from  a  saturated  atmosphere  at  15  degrees  C. 
adsorbed  four  per  cent  when  the  temperature  was  raised  to  .34 
degrees  C.  A  heavier  soil  which  adsorbed  seven  per  cent  in  a  satu- 
rated atmosphere  at  15  degrees  C.  adsorbed  nine  per  cent  at  34 
degrees  C. 

(d)  Organic  Matter  has  a  high  adsorptive  power  for  water, 
especially  in  the  form  of  colloidal  humus.    All  soils  contain  this  in 
small  amounts,  at  least,  while  some  have  several  per  cent,  which 
gives  them  a  high  hygroscopic  capacity. 

(e)  Humidity. — The  changes  in  humidity  of  the  air  cause  a 
variation  of  hygroscopic  moisture  at  the  same  temperature.     If  a 
soil  adsorbs  one  unit  of  moisture  in  a  saturated  atmosphere  at  a 
certain  temperature,  it  will  adsorb  three-fourths 4  of  a  unit  when 
the  air  is  three-fourths  saturated,  and  one-half  unit  at  one-half 
saturation,  but  at  one-fourth  saturation  will  adsorb  slightly  more 
than  this  proportion. 

Dobeneck  has  shown  the  effect  of  various  relative  humidities 
on  the  hygroscopic  content  of  quartz  and  humus  after  an  exposure 
of  24  hours  at  20  degrees  C. 

Percentage  of  Hygroscopic  Moisture  (Dobeneck)  5 


Relative  humidity 
per  cent. 

30 

50 

70 

90 

100 

Quartz     

0.045 

0.053 

0.76 

0.119 

0.175 

Humus            

4.055 

7.765 

10.589 

15.676 

18.014 

The  Determination  of  the  Hygroscopic  Coefficient  of  Soils. 
— The  hygroscopic  coefficient  of  a  ,soil  is  the  amount  of  moisture  it 
will  adsorb  when  exposed  to  a  saturated  atmosphere  for  a  definite 
time  at  a  constant  temperature. 

The  determination  of  the  hygroscopic  capacity  or  hygroscopic 
coefficient  of  soils  is  of  considerable  importance,  since  it  gives  a 
constant  for  the  soil  that  depends  upon  the  internal  surface,  thus 
giving  a  means  of  comparison.  One  of  the  best  methods  for  its 
determination  is  that  of  Briggs,  which  is  to  place  the  soil  in  a  satu- 
rated atmosphere  at  75  degrees  F.,  approximately  24  degrees  C.,  and 
let  it  remain  until  no  further  increase  in  weight  is  shown.  It  is 


HYGROSCOPIC  MOISTURE 


197 


then  dried  at  100  decrees  ('.  The  difference  gives  the  hygroscopic 
coefficient  of  the  soil.  Hilgard  has  used  a  temperature  of  200 
degrees  0.  in  the  determination  of  hygroscopic  capacity,  which 
comes  nearer,  probably,  reaching  the  point  of  absolute  dryness  of 
soil.  In  this  determination  the  soil  should  he  spread  out  in  a  very 
thin  layer,  so  that  as  large  a  surface  as  possible  may  be  exposed 
directly  to  the  saturated  air. 

The  hygroscopic  coefficient  of  soils  may  he  determined  indirectly 
by  using  other  constants  to  which  the  hygroscopic  coefficient  bears 
a  definite  relation.  The-  formnhv  are  as  follows: 


(a)  Hygroscopic   coefficient '  =  wilting  coefficient  X  0.68. 

(b)  Hygroscopic  coefficient  =  moisture  equivalent  x  <>..'J7. 

(c)  Hygroscopic     coefficient  =    (moisture     holding     capacity  - 

*  X  0.234. 

(d)  Hygroscopic    coefficient  =  0.007    sands  +  0.082    silt  +  0.:M) 

-j-  organic  matter). 


21) 

(clay 


For  wilting  coefficient  see  page  212;  mx>isture  equivalent,  page 
202,  and  moisture  holding  capacity,  page  20!). 

The  Use  of  Hygroscopic  Moisture. — It  was  formerly  believed 
that  plants  were  able  to  use  some  hygroscopic  moisture,  but  later 
investigations  seem  to  show  that  this  is  not  possible.  Permanent 
wilting  has  been  taken  as  the  point  at  which  plants  cease  to  obtain 
sufficient  water  from  the*  soil,  and  at  this  point,  they  still  contain 
some  capillary  moisture,  although  the  film  is  quite  thin. 

Determinations  of  the  moisture  content  of  soils  at  wilting  have 
been  made  by  Briggs  and  Shantx,  and  are  given  in  the  following 
table : 

Relation  of  Hygroscopic  Coefficient 7  to  the  Willing  Coefficient 


Hygroscopic 
coefficient 

Wilting 
cot'llicicn 

Coarse  sand     

PIT  cent 

0.5 

prr  cent 

0.1) 

Fine  sand             

1.5 

2.6 

Sandy  loam                

3.5 

4.8 

Fine  sandy  loam 

6.5 

9.7 

Ixvim               

7.S 

Clay  loam                 

11.4 

i  (\:.\ 

Amount  of 

capillary  water 

remaining 


per  rent 

0.4 
1.1 
1.3 


Tn  the  work  of  Briggs  and  Sbantx.  the  determination  of  the 
wilting  coefficient  of  soils  always  shows  the  presence  of  some  capil- 
lary water.  Even  at  the  death  point  of  plants  soils  show  more  than 
the  hygroscopic  water  present. 


198 

Hilgard  8  gives  the  following  uses  of  hygroscopic  moisture  in 
plant  growth:  "  (1)  Soils  of  high  hygroscopic  power  can  with- 
draw from  moist  air  enough  moisture  to  be  of  material  help  in 
sustaining  the  life  of  vegetation  in  rainless  summers  or  in  time 
of  drouth.  It  cannot,  however,  maintain  normal  growth  save  in 
the  case  of  some  desert  plants.  (2)  High  moisture  absorption  pre- 
vents the  rapid  and  undue  heating  of  the  surface  soil  to  the  danger 
point,  and  thus  often  saves  crops  that  are  lost  in  soils  of  low  hygro- 
scopic power." 

QUESTIONS 

1.  What  forces  act  upon  water  in  soils? 

2.  What  forms  of  moisture  are  found  in  soils  as  a  result  of  these  forces? 

3.  Define  hygroscopic  moisture. 

4.  How  does  size  of  particles  affect  the  amount  of  hygroscopic  moisture? 

5.  What  effect  do  colloids  have? 

6.  What  effect  does  temperature  have   on  "hygroscopic  moisture   in  com- 

paratively dry  air? 

7.  What  effect  if  the  air  is  saturated? 

8.  What  effect  does  organic  matter  have  on  hygroscopic  moisture? 

9.  What  relation  exists  between  the  adsorption  of  soils  from  different  de- 

grees of  saturation? 

10.  How  do  the  ratios  of  humidity  and  adsorption  compare  in  the  table  on 

page  196? 

11.  Define  hygroscopic  coefficient. 

12.  How  is  it  determined? 

13.  Can  plants  use  hygroscopic  moisture? 

14.  Which  soil  in  the  table  on  page   197   has  the  highest  hygroscopic  co- 

efficient?   Why? 

15.  Which  contains  the  highest  amount  of  capillary  moisture  after  the  wilt- 

ing coefficient  is  reached  ? 

10.  If  a  clay  loam  soil  weighs  80  pounds  per  cubic  foot,  how  many  tons 
of  unavailable  moisture  is  in  the  soil  to  a  depth  of  two  feet  per 
acre?  (See  table  on  page  197.) 

17.  What  is  the  use  of  hygroscopic  moisture? 

18.  The  wilting  coefficient  of  a   clay  loam   is   10.2   per  cent,  what   is  the 

hygroscopic  coefficient? 

19.  If  the  moisture  holding  capacity  of  a  soil  is  23.2  per  cent,  what  is  the 

hygroscopic  coefficient? 

20.  If  a  soil  contains  83.1  per  cent  of  sand,  8.0  of  silt  and  7.5  of  clay,  what 

is  the  hygroscopic  coefficient? 

REFERENCES 

^riggs,  L.  J.,  Journal  of  Physical  Chemistry,  Vol.  9,  1905,  pp.  017-641. 

*  Hilgard,  E.  W.,  Report  of  the  California  Station,  1892-3-4,  p.  70. 

*  Hilgard,  Soils,  1906,  p.  196. 
4  Op.  Cit.,  p.  198. 

*  Dobeneck,  A.  F.,  Von  Untersuchungen  (iber  das  Absorptionsvermogen  und 

die   Hvgroskopizitiit   der    Bodeukonstituenten.      ForscJi.    a.   d.   Gebiete 

d.  Agri.-Physik.,  Band  XV,  1892,  Seite  103-228. 
•Briggs,  L.  J.,  and  Shantz,  H.  L.,  Bulletin  230,  Bureau  of  Plant  Industry. 

U.  S.  D.  A.,  The  Wilting  Coefficient  for  Different  Plants  and  its  Indi- 

rect  Determination,  1912,  p.  73. 
7  Op.  Cit.,  p.  65. 
»  Hilgard,  Soils,  1906,  p.  200. 


CHAPTER  XVI 

WATER  OF  SOILS 

II.     CAPILLARY  WATER 

THE  most  abundant  and  by  far  the  most  important  form  of  soil 
moisture  is  capillary  or  film  moisture.  It  differs  from  hygroscopic 
moisture  in  that  it  evaporates  at  ordinary  temperatures,  is  not  con- 
densed again  on  the  soil  particles,  and  may  move  from  one  particle 
to  another. 

The  term  capillary  as  applied  to  this  form  of  water  has  arisen 
from  the  fact  that  this  movement  may  be  best  seen  in  very  'small 
capillary  tubes.  When  tubes  are  placed  in  water  the  height  to  which 
it  will  rise  varies  with  the  diameter  of  the  tube. 

Height  of  Capillary  Rise  in  Glass  Tubes 


Diameter  of  tubes 


1.0    nun. 
.1     mm. 


Height  of  water 


15.336  mm. 
153.36    mm. 


.01  mm.  1533.6      mm. 


The  law  expressing  this  action  is  as  follows:  The  height  to 
which  the  water  rises  varies  inversely  as  the  diameter  of  the  tube. 
The  reduction  of  the  diameter  one-tenth  causes  the  water  to  rise 
ten  times  as  high.  The  movement  of  water  in  soils  from  a  free 
water  surface  resembles  somewhat  the  movement  of  water  in  a  large 
number  of  capillary  tubes  of  various  sixes.  In  the  case  of  soils 
where  the  water  rises  from  a  free  water  surface  the  amount  in  the 
soil  varies  inversely  as  the  distance  above  the  free  water.  This 
would  be  exactly  true  of  a  large  number  of  various-sixed  capillary 
tubes.  The  explanation  for  soils  is  not  quite  as  simple,  however, 
as  this  would  indicate. 

Surface  Tension. — Whenever  an  air-water  surface  exists  the 
molecules  of  water  in  the  interior  are  attracted  equally  in  all  direc- 
tions. The  molecules  on  the  surface  are  subjected  to  a  double  but 
unequal  attraction  of  the  water  on  one  side  and  the  air  on  the  other. 
Avbich  has  the  effect  of  producing  a  thin  film  composed  of  the  sur- 
face molecules  which  is  under  tension.  Tf  the  film  is  flat  no  pres- 

199 


200 


SOIL  PHYSICS  AND  MANAGEMENT 


sure  is  exerted  in  any  direction.  If  curved  the  tension  will  cause 
a  pressure  in  the  direction  of  the  center  of  curvature  and  in  pro- 
portion to  the  radius  of  curvature.  The  pressure  is  equal  to  two 
times  the  tension  divided  by  the  radius.  The  greater  the  curvature 
the  less  will  be  the  radius  and  consequently  the  greater  the  pressure. 
If  soil  particles  are  in  contact  the  water  will  be  in  two  forms: 
(1)  as  a  film  around  the  particles,  and  (2)  as  a  waist  between  the 
particles  as  shown  in  figure  90.  The  pressure  is  always  in  the  direc- 
tion of  the  center  of  curvature  and  varies  inversely  as  the  radius. 
The  pressure  of  the  film  around  the  soil  particle  is  inward,  while 
that  of  the  waist  is  outward.  The  force  will  then  be  the  difference 
between  these  two.  As  a  general  rule  the  waist  film  exerts  the 
greater  force  because  it  has  the  greater  curvature  or  the  lesser 
radius.  The  pressure  due  to  difference  of  curvature  is  well  shown 
by  two  soap  bubbles  x  a  and  d  that  have  a  free  air  passage  between 
them  as  in  figure  91.  The  curvature  of  the  smaller,  d,  should  give 


FIG.  90. — Soil  particles  showing  films 
and  waists  of  capillary  water. 


Fia.  91. — Large  and  small  bubble  con- 
nected by  a  tube  6.  The  greater  curvature 
of  d  forces  the  air  into  a  until  the  curva- 
ture of  c  is  the  same  as  a. 


it  greater  pressure.  That  this  is  true  is  shown  by  the  fact  that  the 
air  is  forced  from  it  into  the  larger  bubble,  <z,  till  the  film,  c,  across 
the  end  of  the  tube,  has  a  curvature  the  same  as  that  of  the  large 
bubble. 

If  soil  particles  are  in  contact  so  that  the  water  films  coalesce, 
the  films  will  adjust  themselves  so  as  to  be  in  equilibrium.  If,  how- 
ever, water  is  removed  from  one  of  the  particles,  as  at  d,  the  equilib- 
rium will  be  destroyed,  a  pull  will  be  .set  up  toward  d,  and  water 
will  move  from  other  particles  until  equilibrium  is  restored.  In 
figure  90  the  film  around  d  is  thinner  than  at  a,  and  this  may  make 
a  slight  difference  in  the  curvature  of  the  films,  hut  more  particu- 
larly of  the  waists,  the  curvature  being  much  greater  between  c  and 
d  than  between  a  and  6.  The  greater  outward  force  at  e  and  / 
would  draw  water  from  the  other  films. 

If  water  is  added  at  a  the  equilibrium  will  be  destroyed  and 
readjustment  will  take  place.  The  smaller  the  amount  of  water 
present  in  the  soil  the  greater  will  be  the  curvature  of  the  films 


CAPILLARY  WATER  201 

Moisture  in  Soil  Columns.  —  A  number  of  particles  are  ar- 
ranged vertically  as  in  figure  92.  The  film  around  (1)  is  held 
by  the  attraction  of  that  particle  alone.  The  film  around  (2)  is 
held  by  the  attraction  of  the  particle,  plus  the  outward  pull  of  the 
waist  at  a.  The  water  film  of  (3)  is  held  by  its  own  force,  plus 
those  of  a  and  b.  No.  (4)  is  held  by  its  force,  plus  a,  b,  and  c.  The 
film  of  the  lower  soil  particle  must  be  held  by  the  greatest  force,  and 
as  a  result  this  particle  would  have  the  thickest  film.  If  the  lower 
end  of  the  soil  column  contains  free  water  the  films  may  be  so  thick- 
ened by  the  combined  force  of  the  film  above  that  nearly  all  pore 
spaces  may  be  filled  with  water.  The  pore  spaces  of  the  soil  column 
in  contact  with  the  free  water  may  act  as  tubes. 

Effect  of  Size  of  Soil  Particles.  —  It  will  he  seen  from  this, 
then,  that  the  movement  of  capillary  water  is  due  to  the  difference 
in  curvature  of  the  film,  and  the  greater  the  curv- 
ature the  greater  will  be  the  capillary  pull  or 
pressure.  The  smaller  the  amount  of  water  pres- 
ent in  the  soil,  the  greater  will  be  the  curvature 
of  the  film  between  the  soil  particles.  As  a  gen- 
eral rule,  the  larger  the  number  of  soil  particles 
the  greater  the  number  of  films  present,  and 
consequently  the  greater  pull  will  be  exerted  per 
unit  of  volume  of  the  soil.  Hence  the  water 
in  capillary  tubes  represented  by  a  single  film 
at  the  top  of  the  water  column  will  not  rise  as 
high  as  in  the  soil,  where  the  number  of  films 
is  many  times  greater  than  in  the  tube. 

FIO.   02—  show-in*          r^ne  nt>'rjht<  to  which  the  water  will  rise  de- 
reticiiiiy  th<-  thick-  iH.M(ls  upon  the  difference  between  the  combined 

of    films  in  u  vcr-    J_ 

tical  soil  column.  force  of  the  films  and  the  force  of  gravity  rep- 

resented by  the  weight  of  the  water.  In  coarse-grained  soils, 
where  the  total  film  surface  is  small,  this  force  representing  the 
upward  pull  will  soon  be  overcome  by  the  force  of  gravity  or 
weight  of  water,  and  hence  water  will  not.  rise  very  high.  In  liner- 
grained  soils  where  the  total  surface  of  the  films  is  very  large  it 
will  require  the  weight  of  a  very  high  column  of  water  to  balance 
this  force,  hence  in  fine-grained  soils  water  will  rise  much  higher 
than  in  coarse  soils. 

In  two  soils,  one  fine-grained  and  the  other  coarse,  having  the 
films  of  the  same  thickness  and  the  same  curvature,  there  will  be  no 
tendency  for  water  to  move  from  one  to  the  other  when  brought  in 


ness 


202 


SOIL  PHYSICS  AND  MANAGEMENT 


contact,  although  the  finer-grained  soil  may  have  many  times  the 
moisture  content  of  the  other.  On  the  other  hand,  a  clay  soil  may 
extract  water  from  a  sand  soil  when  in  close  contact,  even  if  the 
clay  contains  several  times  the  amount  of  water  that  the  sand  soil 
does.  The  difference  will  be  clue  to  the  fact  that  in  the  case  of  the 
smaller  soil  particles  in  the  finer-grained  soil  the  water  film  will 
have  a  greater  curvature,  and  hence  will  be  able  to  pull  water  from 
the  sand  soil,  where  the  films  have  less  curvature. 

Moisture  Equivalent.2 — Briggs  and  McLane  designed  a  centrif- 
ugal machine  by  which  moist  soils  could  be  subjected  to  a  force  of 
1000  times  that  of  gravity  or  more.  The  soils  under  this  condition 
would  lose  moisture  until  the  capillary  force  was  in  equilibrium 
with  this  force  of  1000  times  gravity,  when  no  further  loss  would 
take  place.  At  this  point  all  soils  have  films  of  the  same  thickness, 
and  if  the  soils  are  put  in  close  contact  there  is  no  tendency  for 
water  to  move  from  one  soil  to  the  other.  The  capillary  forces  are 
in  equilibrium.  The  per  cent  of  water  present  at  this  point  is 
known  as  the  moisture  equivalent  of  the  soil.  It  is  always  higher 
than  the  wilting  coefficient  and  lower  than  the  optimum  water  con- 
tent. While  not  representing  any  critical  moisture  content,  yet  it 
furnishes  a  very  convenient  constant  for  comparison  of  different 
soils.  The  numerical  value  of  the  moisture  equivalent  depends  upon 
the  internal  surface  of  the  soil.  The  following  table  gives  the 
average  for  some  classes  of  soils : 

Moisture  Equivalents  of  Some  Soil  Classes 2 


Maximum 

Minimum 

Average 

Sands              

7.3 

3.0 

4.9 

Fine  sands                       

10.0 

3.8 

5.6 

Sandy  loams     

18.6 

5.3 

10.4 

Ping  sandy  loams  

21.4 

6.8 

13.0 

20.8 

7.7 

16.5 

Silt  loams                           

26.9 

8.3 

17.1 

Clay  loams             

32.4 

15.1 

21.9 

Clays          

38.4 

19.1 

32.0 

Since  the  moisture  equivalent  bears  a  rather  definite  ratio  to 
other  soil  constants  these  may  be  used  in  its  indirect  determination. 

Determination  of  Moisture  Equivalents  from  Other  Soil 
Constants. — When  the  other  soil  constants,  as  wilting  coefficient, 
hygroscopic  coefficient,  moisture  holding  capacity,  or  mechanical 
analysis,  are  known,  the  moisture  equivalents  may  be  determined 
indirectly  by  the  following  formulae : 


CAPILLARY  WATER  203 

(c)  Moisture  equivalent  =(  Moisture  holding  capacity — 21)   X   .635 
(b)    Moisture  equivalent =  Hygroscopic    coi;Hicient   X    2.71 

(a)    Moisture  equivalent  =  Wilting  coi'-fficient  X  1.84 

(d)  Moisture  equivalent  =  0.02    sand  -f  0.22    silt  +  1.05    clay. 

Movement. — The  movement  of  capillary  water  may  take  place 
in  any  direction,  but  with  slightly  greater  facility  downward  than 
upward  or  sidewise,  because  of  the  aid  of  gravity.  The  rate  and 
height  of  movement  depend  upon  several  factors. 

1.  The  Thickness  of  the  Film. — One  of  the  most  important 
factors  in  capillary  movement  is  the  thickness  of  the  film  of  water 
on  the  soil  particle.  As  a  general  rule,  the  greater  the  difference 
between  the  moisture  content  of  adjacent  soil  masses,  or  the  greater 
the  difference  in  the  thickness  of  films,  the  stronger  will  be  the  pull 
and  the  more  rapid  will  be  the  movement.  This  is  very  well  shown 
in  soils  adjacent  to  free  or  gravitational  water.  The  distribution 
near  the  free  water  takes  place  rapidly  through  capillary  passages, 
while  at  some  distance  the  movement  is  by  means  of  thin  films  and 
slow  surface  distribution.  If  this  movement  is  upward,  it  is  re- 
tarded by  gravity,  but  if  downward,  as  after  a  rain,  the  movement 
becomes  somewhat  rapid,  especially  if  the  films  are  quite  thick. 

To  determine  how  rapidly  or  slowly  water  moves  from  a  moist 
soil  into  a  dry  one,  bury  a  dry  clod  two  or  three  inches  in  diameter, 
in  soil  with  medium  moisture  content,  and  examine  every  three  or 
four  days.  The  movement  is  very  slow.  Two  or  three  weeks  will 
be  required  for  the  clod  to  become  moistened.  It  is  without  doubt 
true  that  the  roots  of  plants  go  after  the  moisture  rather  than  wait 
for  the  moisture  to  move  to  them  by  capillarity.  This  fact  controls 
to  a  large  extent  the  root  development  of  plants.  It  must  be  remem- 
bered that  very  little  capillary  water  used  by  plants  is  drawn  from 
the  water  table  of  the  soil,  which  is  usually  many  feet  beneath  the 
surface.  Plants  sometimes  wilt  when  the  free  water  is  not  more 
than  three  or  four  feet  beneath  the  surface,  which  means  that  the 
moisture  rising  by  capillarity  is  not  sullieicnt  for  the  use  of  the 
plant.  The  fact  that  moisture  moves  so  slowly  through  a  dry  soil 
is  what  makes  dust  mulches  so  effective. 

In  order  to  show  the  rate  of  movement  of  water  through  the 
soil,  after  the  dry  summer  of  ISK'.t,  King,  of  Wisconsin,  collected 
samples  of  soil  to  a  depth  of  five  feet,  and  a  portion  of  the  dry  area 
was  effectually  protected  from  rain  and  snow  and  left  in  this  con- 
dition until  April  the  following  year.  Samples  were  then  collected 


204 


SOIL  PHYSICS  AND  MANAGEMENT 


from  the  covered  and  from  the  exposed  soil  and  the  moisture  con- 
tent determined.    The  results  are  given  in  the  table. 

Water  Per  cent  of  Dry  Soil,  Covered  and  Uncovered,  at  Different  Dates  (King)t 


Original  soil 

Soil  covered 

Soil  uncovered 

Oct.  28,  1889 

April  14,  1890 

April  14,  1890 

1st  foot,  sandy  clay  

per  cent 

4.03 

per  cent 

3.32 

per  cent 

20.23 

2nd  foot,  red  clay  ...          ... 

10.07 

6.68 

20.01 

3rd  foot,  clay  and  sand  

9.11 

6.32 

8.32 

4th  foot,  sand  and  gravel  

4.35 

3.71 

8.63 

5th  foot,  sand  and  gravel  .        ... 

4.53 

5.08 

6.07 

Mean  

6.42 

5.02 

12.65 

In  the  protected  soil  there  was  not  only  no  gain  by  capillarity 
from  the  sides  or  from  below,  but  an  actual  loss  occurred. 

2.  Viscosity. — Viscosity  is  the  resistance  that  liquids  offer  to 
the  movement  of  molecules  against  each  other.  This  property  is 
well  seen  in  s}rrups,  but  we  do  not  ordinarily  think  of  water  as  pos- 
sessing any  large  amount  of  viscosity  or  showing  any  variation 
in  this  respect  under  different  conditions.  A  somewhat  higher 
viscosity  increases  the  surface  tension  of  the  film,  but  at  the  same 
time  retards  the  rate  of  movement  by  lessening  the  fluidity  and 
freedom  of  movement. 

(a)  Temperature.  -  -  Variations  in  the  temperature  of  water 
change  its  viscosity,  a  higher  temperature  diminishing  and  a  lower 
increasing  it.  Increasing  viscosity  increases  surface  tension.  It 
has  been  determined  that  if  the  viscosity  of  water  at  zero  C.  is  taken 
as  100,  then  the  viscosity  at  25  degrees  is  50,  at  30  degrees  45,  and 
at  50  degrees  31.*  This  variation  influences  the  capillary  move- 
ment of  moisture  in  soils  to  some  extent. 

The  next  table  shows  that  capillary  movement  is  more  rapid  at 
higher  temperatures,  indicating  that  the  greater  fluidity  produced 

Effect  of  Temperature  on  Rise  of  Capillary  Moisture,9  University  of  Illinois. — 
Height  in  Inches  in  24  Hours 


Temperature,  degrees 
Fahrenheit 

Brown  silt 
loam 

White  silt 
loam 

Yellow  fine  sandy 
loam 

32.5 
60.5 
70.5 

11.9 
13.3 
13.5 

11.9 
14.0 
14.5 

19.7 
22.9 

25.8 

CAPILLARY  WATER  205 

is  of  greater  importance  than  an  increased  tension,  at  least  within 
the  limits  of  the  experiment.  While  an  increase  in  viscosity  gives 
greater  surface  tension,  the  rate  of  movement  is  decreased  becau.se 
of  greater  resistance.  Under  higher  teni}>eratures  the  capillary 
limit  would  be  reached  sooner,  yet  the  height  attained  would  be 
less  than  at  lower  temperatures. 

Somewhat  dry  soils  frequently  become  moist  in  late  autumn 
without  rain.  This  is  probably  duo  to  two  things — less  evap- 
oration due  to  lowering  of  temperature  and  increased  capillary  pull 
at  the  surface  due  to  greater  surface  tension  of  the  water  at  this 
temperature. 

(b)  Substances  in  Solution. — The  viscosity  and  likewise  the 
surface  tension  of  water  are  affected  more  or  less  by  substances  in 
solution.  Some '  increase,  while  others  decrease  tension.  The 
height  to  which  liquids  rise  in  soils  varies  with  the  surface  tension, 
the  densities  of  the  liquids  being  the  same.  The  rapidity  of  rise 
of  those  liquids  in  the  same  soil  depends  upon  the  viscosity :  the 
more  viscid  the  liquid  the  slower  the  movement.  Mineral  sub- 
stances added  to  a  soil  generally  increase  the  surface  tension.  If 
potassium  chloride  is  added  to  the  surface  of  a  soil  the  capillary 
pull  of  the  surface  moisture  will  be  increased,  and  more  water  will 
be  brought  up  from  the  subsoil.  This  is  true  of  most  mineral 
fertilisers. 

Organic  substances  lower  the  surface  tension  so  that  they  would 
not  cause  so  great  capillary  pull,  but  would  increase  the  rapidity  of 
movement.  Soil  solutions  have  a  low  surface  tension. 

Rains  wetting  a  few  inches  in  depth  have  a  tendency  to  draw 
water  up  from  the  deeper  soil,  as  observed  by  King.-"'  He  found 
that  .'}.">  pounds  per  square  foot  in  one  trial  and  .'5.0!)  in  another 
had  been  transferred  from  the  lower  soil  '2\  to  18  inches  to  the  upper 
in  20  hours  after  wetting.  This  is  due  in  part  to  the  fact  that  the 
surface  tension  of  rain  water  is  greater  than  that  of  soil  solutions. 

From  the  next  table  it  will  be  seen  that  common  salt  gives  the 
greatest  tension  and  that  soil  solutions  are  low.  If  any  of  the 
chemical  substances  mentioned  in  the  table  should  be  applied  to 
the  surface  of  the  soil  when  it  passed  into  solution,  the  tension 
would  be  increased  sufficiently  to  draw  up  water  from  below.  Some 
recent  experiments  by  Karraker  *  indicate  that  substances  in  solu- 
tion play  little  part,  in  moisture  movement.  The  strengths  of  the 
solutions  in  the  table  are  much  greater  than  probably  ever  occur 
in  soils,  unless  it.  should  be  in  the  immediate  surface  just  after  an 


206 


SOIL  PHYSICS  AND  MANAGEMENT 


Surface  Tension  and  the  Density  of  Certain  Solutions  7 


Solution 

Density 

Surface 
tension,  dynes 
per  .-'i-  cm. 

Water  

1.0000 

739 

Common  salt  (NaCl)  

1.1000 

77.6 

Muriate  potash  (KC1)  

1.1000 

77.5 

Ammonium  sulfate  ((NH  4)280.1)  

1.1000 

768 

Sodium  sulfate  (Na2SO4)  

1.1000 

75.8 

Sodium  nitrate  (NaNO-0  

1.1000 

75.8 

Potassium  hydrate  (KOH)  

1  1000 

75  1 

Potassium  sulfate  (K-..SO4)  

1.0830 

75.1 

Wood  ashes  

1  0038 

75.2 

Thomas  slag                

1  0012 

774 

Marl  

1.0013 

77.0 

Lime       .          

1.0020 

755 

4mmonia  (NH4OH)     

09600 

675 

Urine  

1.0260 

64.9 

Stable  manure     

1.0013 

732 

Kentucky  blue-grass  soil  

1  0000 

71  0 

Wheat  soil                                     .        .    . 

1  0000 

69  6 

Garden  soil  

1.0000 

69  4 

application  of  some  mineral  fertilizer  or  in  alkali  soils.     In  either 
of  these  cases  some  effect  would  undoubtedly  be  produced. 

3.  Texture.  -     The  smaller  the  soil  particles  the  slower  the 
capillary  movement,  but  theoretically  the  higher  the  water  will 
rise.     This  is  true  only  in  theory.     The  resistance  to  movement 
becomes  so  great  in  very  fine-grained  soils  that  the  water  will  not 
rise  as  high  as  in  medium-grained  ones.     Loughridge  found  that 
in  an  adobe  soil  with  44.3  per  cent  of  clay,  a  height  of  46  inches 
was  reached  in  195  days,  while  in  a  fine  sandy  soil  the  water  attained 
a  height  of  47  inches  in  125  days.    In  a  sand  soil  the  water  reached 
its  limit  in  six  days.     The  movement  of  water  in  clay  soils  is  very 
slow,  not  only  due  to  the  extreme  fineness  of  the  ordinary  clay 
particles,  but  to  the  presence  of  colloids  which  doubtless  hinder 
the  movement. 

In  experiments  with  two  soils  water  rose  by  capillarity  8.5  feet 
in  90  days  in  loess  (yellow  fine  sandy  loam),  while  in  white  silt 
loam  soil  with  0.8  per  cent  of  organic  matter  it  rose  9.5  feet  in  about 
the  same  time.  The  loess  contained  practically  no  organic  matter. 

4.  Organic  Matter. — The  presence  of  organic  matter  retards 
capillary  movement,  due  to  the  colloids  present  and  the  greater 
porosity  produced.     The  next  table  shows  the  movement  of  water 
in  soils  by  capillarity  from  a  free  water  surface.     The  tubes  were 
one  and  one-half  inches  in  diameter  and  five  feet  long. 


CAPILLARY  WATER 


207 


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208 


SOIL  PHYSICS  AND  MANAGEMENT 


By  comparing  columns  1  and  2,  3  and  4,  5  and  (>,  7  and  8,  9  and 
10,  and  then  all  with  11  in  the  table,  the  effect  of  organic  matter 
may  be  seen. 

In  the  coarse-grained  soils  the  organic  matter  which  consisted 
of  finely  ground  well-decomposed  peat  gives  a  greater  range  of 


• 


„„    s,,, 


I 


Flo.  93. — Showing  the  effect  of  various  amounts  of  organic  matter  on  the  rise  of  capillary 
water  from  a  free-water  surface  for  a  14-day  period. 


CAPILLARY  WATER 


209 


movement.  It  reduces  the  rapidity  at  first,  but  the  water  in  the 
mixture,  as  shown  in  column  No.  2,  passes  Xo.  1  in  six  hours.  In 
the  finer-grained  soil  the  effect  of  organic  matter  is  to  not  only 
retard  the  movement  from  the  first,  hut  to  diminish  the  height,  as 
shown,  by  comparing  Xos.  3  and  4,  5  and  0,  and  7  and  8.  A  com- 
parison of  Xos.  9  and  10  shows  the  effect  of  the  removal  of  organic 
matter  by  cropping.  Slow  capillary  movement  is  desirable  in  sur- 
-face  soils  to  prevent  excessive  loss  of  moisture  by  evaporation.  The 
subsurface  and  subsoil  are  better  adapted  for  more  rapid  capillary 
movement  which  brings  the  moisture  up  where  roots  in  the  surface 
soil  may  obtain  their  supply.  The  peat  is  an  excellent  example  of 
very  slow  movement  through  a  very  porous  soil.  The  limit  was 
reached  in  ten  days.  Figure  93  shows  the  effect  of  organic  matter 
on  height  of  rise  of  water. 

Maximum  Capillary  Capacity  or  Moisture-holding  Ca- 
pacity of  Soils. — Soils  possess  varying  powers  of  retaining  moist- 
ure- by  capillarity  due  primarily  to  texture.  The  method  of  deter- 
mining this  has  been  devised  by  Hilgard  and  modified  by  Briggs. 
A  small  cup  five  centimeters  in  diameter  and  one  in  height, 
with  the  l)ottom  made  of  very  fine  bolting  cloth,  is  used.  The  soil 
is  settled  slightly  by  jarring  and  stroked  off  level  with  the  top  of 
the  cup.  It  is  then  placed  with  the  bottom  in  the  water,  and  when 
the  soil  has  taken  up  the  maximum  amount  of  water,  it  is  allowed 
to  drain  for  a  few  minutes,  and  the  weight  of  the  water  determined 
by  comparing  with  the  weights  of  the  dry  soil.  This  weight  is  des- 
ignated as  the  water-holding  capacity  of  the  soil.  This  is  much 
higher  than  will  be  found  under  field  conditions.  The  following 
table  shows  the  percentage  of  water  held  by  capillarity  and  the  total 
water  at  saturation  in  some  soils,  all  from  Illinois  except  the  last. 

Maximum  Capillary  and  Maximum  Water  Cajmcity  9 


Held  by 
capillarity 

Total 

water 

Kxrp.ss  of  total 
over  capillarity 

Sand 

per  mil 

27  SO 

per  rent 

2<)  23 

per  crnt 

1  43 

Ycllow-grav  silt  loutn 

4")  42 

4S.SS 

3.40 

Yellow  silt  loam 

48.31 

52.10 

3.79 

Brown  silt  loam   

00.04 

<>4.f>0 

4.o2 

Black  clay  loam 

00.00 

69.32 

2.66 

Palouse  volcanic  ash  soil  

00.00 

64.49 

4.49 

14 


210 


SOIL  PHYSICS  AND  MANAGEMENT 


Amount  of  Water  Moved  by  Capillarity. — The  many  experi- 
ments made  indicate  the  movement  of  large  amounts  of  water  by 
surface  tension.  King  used  a  fine  sand  taken  from  the  subsoil  and 
a  clay  loam  in  cylinders  four  feet  high,  each  with  a  section  equiva- 
lent to  one  square  foot.  The  soils  were  completely  saturated  and 
the  cylinders  were  placed  so  that  the  water  level  was  one  foot  below 
the  surface.  A  strong  current  of  air  was  passed  over  the  surface 
for  eight  days  and  the  evaporation  determined.  The  same  thing 
was  done  with  the  water  level  at  two,  three,  and  four  feet  below  the 
surface. 

Water  Evaporated  Daily  Per  Square  Foot  with  the  Water  Level  at  Different 
Distances  Below  the  Surface  10 


Kind  of  soil 

One  foot 

Two  feet 

Three  feet 

Four  feet 

Fine  sand     

pounds 
2.37 

pounds 

2.07 

pound* 
1.23 

pounds 

0.91 

Clay  loam 

2.05 

1.62 

1.00 

0.90 

These  results  show  that  the  amount  of  water  raised  four  feet 
was  equivalent  to  one  inch  of  rain  in  five  and  one-half  days.  From 
such  experiments  the  impression  is  given  that  capillarity  is  the 
great  factor  in  bringing  water  to  the  crop.  It  does  play  a  large  part, 
but  the  conditions  in  the  above  experiment  were  much  more  favor- 
able than  are  ordinarily  found  in  the  field.  The  water  rose  from  a 
free-water  surface  and  the  artificial  breeze  increased  evaporation 
enormously.  Capillary  movement  is  extremely  slow  through  clay 
loam,  and  it  is  very  likely  that  the  water  evaporated  from  that  soil 
when  the  water  table  was  36  or  48  inches  below  the  surface  was  not 
obtained  from  the  water  table,  but  from  the  reserve  in  the  soil.  It 
takes  more  than  eight  days,  as  seen  in  the  table,  page  207,  for  water 
to  be  carried  48  inches  or  even  36  inches  in  height.  The  results  are 
without  doubt  much  higher  than  would  be  obtained  under  normal 
field  conditions.  In  regard  to  capillary  movement,  Rotmistrov,11 
of  Russia,  says,  "As  regards  the  mechanical  raising  of  water,  how- 
ever, by  capillary  action,  it  may  be  assumed  that  the  limit  from 
which  water  can  make  its  way  upward  lies  much  higher  than  the 
limit  accessible  to  roots.  All  the  data  at  my  command  regarding 
moisture  in  the  soil  of  the  Odessa  experimental  field  point  only  to 
one  conclusion,  namely,  that  water  percolating  beyond  a  depth  of 
40  to  50  centimeters  (16  to  20  inches)  does  not  return  to  the  surface 
except  by  way  of  roots." 


CAPILLARY  WATER 


211 


The  evaporation  from  the  lysimeters  or  drain  gages  at  Koth- 
anisted,  England,  from  bare  soil  at  depths  of  20  inches  and  60 
inches,  shows  an  excess  of  0.11  of  an  inch  per  annum  for  the  deeper 
soil  mass  as  an  average  for  34  years.  This  represents  the  water 
brought  to  the  surface  from  the  40  inches  of  subsoil  of  the  deeper 
gage,  and  amounts  to  only  12  tons  per  acre  per  annum,  or  not  suffi- 
cient to  grow  more  than  one-half  bushel  of  wheat.  This  indicates 
tbat  a  very  small  amount  cf  water  is  brought  from  a  depth  greater 
than  20  inches  by  capillarity  in  a  clay  loam  soil. 


Rainfall  and  Evajmralion  at  Rothamsted,  England, n  Average  fm  34  Yearn, 

1871  to  1.904 


Rainfall, 
inches 

Evaporation  (or  retained  by  soil) 

20  inches 

40  inches 

00  inches 

January 

2.32 

1.97 
1.83 
1.89 
2.11 
2.36 
2.73 
2.67 
2.52 
3.20 
2.86 
2.52 

0.50 
0.55 

0.96 
1.39 
1.62 
1.73 
2.04 
2.05 
1.64 
1.35 
0.75 
0.50 

0.27 
0.40 
0.81 
1.32 
1.56 
1.71 
2.03 
2.05 
1.69 
1.36 
0.68 
0.37 

0.36 
0.49 
0.88 
1.36 
1.61 
1.74 
2.08 
2.09 
1.76 
1.52 
0.82 
0.48 

February 

March   

April 

May  

June                     .      .  . 

July  

August        

September         

October     

November         

December 

Total  nor  vear  .  . 

2S.9S 

15.08 

14.25 

15.19 

Results  for  maximum  and  minimum  rainfall 


Maximum  (1903) 
Minimum  (1898). 


38.69 
20.49 


15.21 
13.17 


15.09 
12.59 


14.46 
12. SO 


The  Capillary  Pull  of  Soils. —  It  is  quite  important  to  be  able 
to  measure  this  capillary  force  for  different  soils.  A  method  for 
doing  this  lias  been  devised  by  Lynde  and  Dupre.  It  consists  of 
placing  the  soil  in  a  funnel  on  a  cotton  cloth  filter  that  is  con- 
nected with  a  water  column  by  means  of  a  wick.  The  water  column 
rests  upon  a  column  of  mercury,  the  lower  end  of  which  is  in  a 
vessel  of  mercury.  As  the  water  evaporates  from  the  surface  of  the 
soil  the  water  in  the  tube  rises  and  with  it  the  mercury.  The  height 
of  the  mercury  represents  the  pull.  The  capillary  lift  is  quite  large 


212 


SOIL  PHYSICS  AND  MANAGEMENT 


in  fine-grained  soils,  as  shown  in  the  next  table,  and  would  be  suffi- 
cient to  sustain  a  column  of  water  of  the  height  given  in  the  third 
column. 

The  Capillary  Lift  of  Soil  Constituents  " 


Soil  constituent 

Diameter  of  grains 

Height  of  H,0 

Medium  sand  

mm. 

.5     -.25 

feet 
.98 

Fine  sand     

.25  -.1 

1.78 

Very  fine  sand     

.1     -.05 

4.05 

Silt  

.05  -.005 

9.99 

Clay  

.005 

26.80 

Osmosis  in  Soils. — Lynde  and  Dupre  14  have  demonstrated 
that  soils  containing  fine  particles  act  as  semi-permeable  membranes, 
probably  producing  only  a  fractional  part  of  the  pressure  of  a  mem- 
brane. Movement  of  this  kind  takes  place  when  a  difference  in 
concentration  of  solutions  exists  in  adjacent  soil  masses.  The  direc- 
tion of  movement  is  toward  the  point  or  zone  of  greatest  concentra- 
tion. The  osmosis  is  increased  by  a  higher  temperature,  so  that  the 
movement  is  greater  in  summer  than  winter. 

King in  has  found  that  manure  incorporated  with  soil  caused  a 
rise  of  water  into  the  upper  three  feet  of  soil,  due  to  a  stronger  solu- 
tion and  greater  osmotic  pressure.  Fertilizers  when  applied  to  a 
soil  dissolve  and  cause  a  greater  concentration  of  the  soil  solution 
as  well  as  a  greater  surface  tension,  with  the  result  that  water  is 
drawn  to  the  surface.  It  is  probably  true  that  tillage  and  the  appli- 
cation of  lime,  both  of  which  may  aid  bacterial  action  in  developing 
plant  food  and  thus  producing  stronger  soil  solutions,  may  promote 
better  surface  moisture  conditions. 

Use  of  Capillary  Water. — Capillary  water  is  the  form  used  by 
plants  in  their  growth.  Even  in  the  most  severe  drouths  plants 
cannot  extract  all  of  the  film  moisture.  The  common  crops  may 
use  some  gravitational  water,  but  only  to  a  very  slight  extent.  Rice 
and  cranberries  are  naturally  adapted  to  growth  in  a  very  wet  or 
even  saturated  soil.  The  amount  of  water  in  a  soil  for  best  growth 
varies  within  rather  wide  limits,  but  our  common  crops  make  best 
growth  when  soils  contain  from  40  to  60  per  cent  of  their  total 
moisture  capacity.  This  is  the  optimum  water  content. 

Wilting  Coefficient.16 — The  moisture  content  of  the  soil  at 


CAPILLARY  WATER 


213 


which  the  plant  wilts  permanently  or  at  which  it  cannot  maintain 
its  rigidity  is  the  uniting  coefficient.  This  point  does  not  vary  a 
great  deal  with  different  plants,  not  often  over  three  per  cent  and 
usually  within  1.5  per  cent.  It,  however,  varies  widely  with  different 
soils.  The  work  of  Briggs  and  Shantz  shows  that  it  is  approxi- 
mately one  and  one-half  (1.47)  times  that  of  the  hygroscopic  coeffi- 
cient. It  represents  the  lower  limit  of  available  moisture.  In 
sands  and  light  sandy  loams  in  which  the  hygroscopic  coefficient  is 
very  low  the  wilting  coefficient  is  also  low.  In  clay  soils  whose 
hygroscopic  coefficient  varies  from  12  to  20  per  cent  the  wilting 
coefficient  is  from  18  to  30  per  cent,  while  in  muck  and  peat  soils 
it  may  run  as  high  as  70  per  cent.  The  wilting  coefficient  of  the 
same  soil  is  a  constant  that  may  he  used  in  the  determination  of 
other  constants,  such  as  the  hygroscopic  coefficient  and  water-hold- 
ing capacity. 

The  wilting  coefficient  is  determined  experimentally,  hut  may 
also  he  found  indirectly  from  other  soil  constants  to  which  it  sus- 
tains a  definite  relation.  The  following  formula1  mav  he  used: 


(a)  Wilting  Coefficient  = 


Moisture  equivalent 
1.84 


n  \ 
(b) 


-ur-i.-      r*     a-  •  Hygroscopic  Coefficient 

Wilting  Coefficient  =  ~I\RQ~ 


(c)  Wilting  Coefficient  = 


Moisture  holding  capacity 
2.90 


(d)  Wilting  Coefficient  =  0.01  sands  +  0.12  silt  +  0.57  clay 

The  probable  errors  have  been  omitted  from  these  formulae. 
Willing  Coefficients  of  Various  Soils  for  Different  Plants  l7 


Course 
sand 

Fine 
sand 

Sandy 
loam 

Loam 

Clay 

loam 

Corn  

1.07 

3.4 

6.6 

10.2 

15.5 

Sorghum 

95 

3.3 

5S 

9.7 

139 

Wheat  (Kuhanka)  .  .  . 

.88 

3.3 

6.3 

10.3 

14.5 

Oats  

1.01 

3.1 

6  1 

10.5 

149 

Barley  

1.04 

2.9 

6.2 

10.5 

14.2 

KVe  

.1)1 

2.9 

5.9 

9.6 

11.4 

Rice  (Japan)  

.96 

2  7 

5.6 

10.1 

13.1 

Squash  
Pea  (Canada)  

1.21 

1  .02 

2.6 
3.3 

6.4 
6.9 

9.4 
12.4 

15.1 
16.6 

Vetch    .  . 

1  22 

24 

<)  1 

9.7 

14  7 

Tomato  

1.11 

3.3 

6.9 

11.7 

15.3 

Clover  (red)  

1.00 

10.7 

Moisture  equivalent. . . .       1.55 


12.0 


1S.9 


27.4 


214 


SOIL  PHYSICS  AND  MANAGEMENT 


Available  Moisture. — The  non-available  moisture  is  that  per 
cent  found  in  Soils  when  permanent  wilting  occurs.  It  is  possible 
that  a  small  amount  of  this  may  be  slowly  available  but  insufficient 
for  rapid  or  even  normal  growth.  It  is  supplied  to  the  plant  much 
too  slowly.  When  the  capillary  force  equals  the  osmotic  pressure 


Water  offydration 
Wafer  free  (at/oo'C.) 


Unavailable  < 
Moisture 


Available 
Moisture 


(Jnavai/able 
Moisture 


^      I 

-f-  r    Hygroscopic  Coefficient 
Wiltinq  Coefficient 

>•    Moisture  Equ/ro/ent 

Optimum  Moisture   Content 


for  Ordinary  Crops 


Moisture  Holding  Capacity 


Completely  Saturated 


Fia.  94. — Diagram  showing  the  relation  of  different  forms  of  moisture  to  the  available  and 
unavailable  moisture  of  soils. 

or  force  of  the  plant  the  water  may  be  said  to  be  non-available. 
The  difference  between  the  wilting  coefficient  and  the  maximum 
capillary  capacity  gives  the  maximum  amount  of  available  water. 
Somewhere  between  these  lies  the  critical  or  optimum  water  con- 
tent. Under  field  conditions  the  difference  between  the  amount  of 


CAPILLARY  WATER  215 

moisture  contained  and  the  wilting  coefficient  will  give  the  avail- 
ahle  moisture.  A  small  amount  of  gravitational  moisture  may  be 
used  by  plants.  Ordinary  plants  live  but  make  little  growth  when 
the  soil  is  saturated.  The  diagram  (Fig.  94)  shows  the  relation  of 
the  soil  constants  and  the  different  forms  of  moisture. 

QUESTIONS 

1.  How  does  capillary  moisture  differ  from  hygroscopic? 

2.  (Jive  law  governing  height. 

3.  What  causes  the  film  on  a  water  surface? 

4.  Under  what  conditions  will  the  Him  exert  pressure? 

5.  If  the  tension  of  water  film  is  73.!)  dynes  per  square  centimeter,  what 

pressure  will  the  film  exert  if  the  radius  of  curvature  is  2.5  mm.? 

6.  Explain  the  movement  of  moisture  from  one  soil  particle  to  another. 

Illustrate. 

7.  How    is  moisture   held    in   soil   columns?     Why   is   the   film   thicker   on 

the  lower  particles? 

8.  What  effect  does  fineness  of  particles  have  on  capillary  pull? 
!>.  What  determines  the  height  to  which  water  will  rise  in  soils? 

10.  Why   should   a  clay   with   a   higher   moisture  content  than   a  sand   soil 

extract  moisture  from  the  latter  when  in  close  contact  with  it? 

11.  What  is  the  moisture  equivalent  of  soils? 

12.  Why  should  clay  have  such  a  high  moisture  equivalent  compared  with 

other  soils? 

13.  Find  the  moisture  equivalent  if  the  hygroscopic  coefficient  is  0.3  per  cent. 

14.  What  determines  the  rapidity  of  capillary  movement? 

15.  What  is  the  significance  of  the  experiment  with  the  clod? 

10.  What  effect  does  capillary  movement  have  on  root  development? 

17.  (Jive  King's  experiment  with  the  covered  soils. 

18.  Define  viscosity.      What  effect   on    surface   tension   does    it    have?      On 

capillary  movement? 
10.  What  effect  does  temperature  have  on  capillary  movement?     Why? 

20.  What    effect    do    mineral    sul>stances    in    solution    have    upon    tension? 

Organic  substances? 

21.  What  effect  will  an  application   of  manure  have  on  surface  tension? 

22.  Why  does  water  rise  faster  in  medium-  than  fine-grained  soils? 

53.  Compare  columns  1.  3,  and  5  in  the  table  on  page  207  and  explain  dif- 
ferences. 

24.  Compare  !>,   10,   11.  and    12  and  explain  differences. 

25.  From  the  standpoint  of  capillary  movement,  is  organic  matter  desirable 

in  soils? 
2f>.  How   is  the  maximum   capillary   capacity  of  soils  determined? 

27.  What  about  the  delivery  of  large  amounts  of  water  by  capillarity   for 

crops  ? 

28.  Hive  the  conclusions  reached  from  the  drain  gaires  at   Rothamsted. 
20.  Describe  the  method  of  determining  capillary  pull  of  soils. 

30.  Will  water  rise  20.8  feet  Hgh  in  clav? 

31.  What  part  does  osmosis  plav  in  moisture  movement? 

32.  f!ive  uses  of  capillary  moisture. 

33.  What  is  the  wilting  coefficient  ? 

34.  If  (lie   hygroscopic  coefficient    is  0.2   per  cent,  what    is  the   wilting  co- 

efficient ? 

35.  What  is  meant  hv  available  moisture? 


216  SOIL  PHYSICS  AND  MANAGEMENT 

36.  How  do  different  soils  compare  in  the  amount  of  available  moisture? 

37.  A  soil  in  the  field  contains  26.3  per  cent  of  moisture  and  the  hygro- 

scopic coefficient  is  6.5  per  cent.     How  much  available  moisture  does 
the  soil  contain? 

REFERENCES 

1  Briggs,  L.  J.,  Yearbook,  U.  S.  D.  A.,  1898,  p.  399. 

I  Briggs,   L.  J.,   and  MoLane,  J.   W.,   The  Moisture  Equivalents  of   Soils, 

Bulletin  45,  Bureau  of  Soils,  U.  S.  D.  A.,  1907. 

3  King,  F.  H.,  Wisconsin  Station,  7th  Ann.  Report,  p.  144. 

4  Smithsonian  Physical  Tables,  1896,  p.  136. 
"King,  F.  H.,  Physics  of  Agriculture,  1901,  p.  170. 
'Unpublished  data,  Soil  Physics  Division,  University  of  Illinois. 
7Lyon,  T.  L.,  and  Fippin,  E.  O.,  Soils,  1909,  p.  160. 

8  Karraker,   P.   E.,   Journal  of   Agricultural  Research,   Vol.   4,  No.   2,   pp. 

187  to  192. 

'Unpublished  data,  Soil  Physics  Division,  University  of  Illinois. 
"King,  F.  H.,  Wisconsin  Station,  7th  Ann.  Report,  p.  151. 

II  Rotmistrov,  V.  G.,  Nature  of  Drought  According  to  the  Evidence  of  the 

Odessa  Experiment  Station,  Russia,  English  edition,  1913. 

"  Hall,  A.  D.,  The  Book  of  the  Rothamsted  Experiments,  1905,  p.  23. 

"Lynde,  C.  J.,  and  Dupre",  H.  A.,  Jour.  Am.  Soc.  Agron.,  Vol.  5,  No.  2,  1913, 
p. 111. 

14  Lynde,  C.  J.,  and  Bates,  F.  W.,  Proceedings  Am.  Soc.  Agron.,  Vol.  4,  pp. 
102-122.  Lynde,  C.  J.,  and  Dupre,  H.  A.,  Jour.  Am.  Soc.  Agron.,  Vol. 
5,  No.  2,  Vol.  7,  Nos.  1  and  6. 

"  King,  F.  H.,  Physics  of  Agriculture,  1907,  p.  172. 

lfl  Briggs,  L.  J.,  and  Shantz,  H.  L.,  Bulletin  230,  Bureau  of  Plant  Industry, 
U.  S.  D.  A.,  The  Wilting  Coefficient  for  Different  Plants  and  Its  In- 
direct Determination,  1912,  p.  72. 

"Op.  Cit.,  pp.  26-33. 

General  Reference — Briggs,  L.  J..  Bulletin  10,  Division  of  Soils,  U.  S. 
D.  A.,  Mechanics  of  Soil  Moisture,  1897. 


CHAPTER  XVII 
WATER  OF  SOILS 

III.    GRAVITATIONAL  WATER 

GRAVITATIONAL  water  is  that  which  may  be  removed  from  the 
soil  by  the  force  of  gravity  or  drained  from  the  soil  under  normal 
conditions.  The  possible  amount  of  the  gravitational  water  is  the 
difference  between  the  water  held  by  a  soil  at  its  maximum  capil- 
lary capacity  and  at  its  maximum  water  capacity,  when  completely 
saturated,  or  when  the  air  space  is  completely  filled.  This  amount 
varies  with  the  type  of  soil. 

The  determination  of  the  gravitational  water  capacity  of  soils 
is  very  unsatisfactory.  The  amount  depends  upon  the  height  above 
the  water  table.  The  gravitational  water  is  the  difference  between 
the  water  content,  when  completely  saturated,  and  when  only  satis- 
fied with  capillary  water.  This  amount  will  vary,  since  the  same  soil 
will  be  satisfied  by  a  smaller  amount  of  capillary  water  the  greater 
the  distance  above  the  water  table.  King  shows  the  amount  of 
water  at  different  heights  above  the  water  table  with  sands  of  dif- 
ferent grades  and  two  soils. 


Water  at  Different  I  frights  Abort 


(he  Water  Table  After  Keing  Saturated  and 
Drained  l 


llriirht  above 
water  table 

Hand  No.  20 

Sand  No.  (»() 

Sand  No.  UK) 

Sandy  loiini 

Clay  loam 

inches 

per  cent 

;«•;•  cent 

l>cr  cent 

l>rr  cent 

per  cent 

84-81 

.23 

.61 

3.93 

16.16 

21.16 

72-69 

1.18 

1  .SO 

4.94 

16.55 

31.05 

00-.r)7 

1.83 

2.26 

6.77 

17.59 

31.21 

48-45 

2.03 

2.46 

10.50 

IS.  70 

31.99 

36-33 

2.31 

4.10 

14.95 

20.90 

32.45 

24-21 

3.42 

13.52 

1S.92 

21.46 

34.40 

12-  9 

16.08 

22.46 

22.6S 

22.6S 

35.97 

6-  3 

20.96 

22.SS 

30.28 

27.69 

37.19 

Percolation. ---The  movement  of  gravitational  water  downward 
through  the  soil  bv  the  force  of  gravitv  is  called  percolation.  It 
depends  upon  several  factors. 

1.  Physical  Composition  or  Texture. — The  movement  of 
water  through  the  soil  bv  the  force  of  gravity  varies  directly  as  the 

217 


218  SOIL  PHYSICS  AND  MANAGEMENT 

size  of  the  particles  and  the  pore  spaces,  but  inversely  as  the  total 
pore  space  or  the  porosity.  Since  these  factors  depend  upon  the 
size  of  the  particles,  the  physical  composition  is  the  controlling 
factor  in  percolation.  If  a  fine-grained  soil  has  50  per  cent  of  pore 
space  and  a  coarse-grained  one  has  33,  it  must  follow  that  the  pore 
spaces  in  the  former  must  be  infinitely  more  numerous  and  smaller 
than  in  the  latter.  If  the  average  diameter  of  the  particles  of  the 
fine-grained  soil  is  0.01  mm.  and  of  the  other  1  mm.,  the  number 
of  pores  for  equal  areas  will  be  approximately  10,000  times  more 
numerous  in  the  fine  than  in  the  coarse,  and  consequently  the  resist- 
ance to  the  movement  of  the  water  would  be  much  greater  in  the 
fine-grained  soil  or  through  the  smaller  pores.  The  nearer  the  par- 
ticles approach  uniformity  in  size  the  more  favorable  the  conditions 
for  percolation.  If  various  sized  particles  are  present  and  of  sim- 
ilar shapes  the  smaller  ones  may  tend  to  clog  the  interspaces  between 
the  larger  and  may  render  the  soil  impervious.  If  the  particles 
are  very  irregular  in  shape,  regardless  of  size,  the  permeability  of 
the  soil  may  be  increased.  This  is  true  of  volcanic  ash  soils.  The 
structure  of  the  soil  is  an  important  factor  in  percolation. 

2.  Granulation. — In  the  case  of  clays  and  other  fine-grained 
soils  the  cementing  of  the  soil  particles  into  granules  aids  percola- 
tion.    The  large  interspaces  existing  between  the  granules  allow 
free  movement.     Even  in  soils  with  considerable  amounts  of  sand 
percolation  may  be  aided  by  granulation.     Heavy  soils  devoid  of 
granules  are  almost  absolutely  impervious.    Such  soils  are  puddled. 
They  may  be  so  naturally,  or  they  may  become  so  by  some  mechani- 
cal operation,  such  as  plowing  or  tramping  of  stock  when  wet. 
This  condition  may  be  only  temporary. 

Any  substance  that  causes  or  aids  granulation  will  increase  per- 
meability and  consequently  percolation.  The  application  of  lime, 
chalk,  marl,  or  limestone  to  clay  soils  is  a  well-known  practice  for 
producing  better  tilth.  Clay  soils  are  readily  permeable  to  water 
only  when  their  colloids  are  in  a  flocculated  condition. 

3.  Organic  Matter. — A  very  favorable  effect  is  produced  upon 
the  permeability  of  medium-  and  fine-grained  soils  by  the  incorpo- 
ration of  organic  matter,  but  in  coarse-grained,  sandy  soils  the  effect 
of  organic  matter  is  to  retard  percolation,  a  thing  very  desirable  in 
such  soils.     In  silt  and  clay  soils  the  irregular  fragments  of  unde- 
composed  parts  of  plants  impart  a  porosity  helpful  to  the  downward 
movement  of  water,  while  the  humified  material  aids  in  the  pro- 


GRAVITATIONAL  WATER  219 

duction  of  cracks  through  its  property  of  shrinkage  as  well  as  its 
effect  on  granulation,  both  favoring  the  movement  of  water. 

4.  Viscosity. — Changes  in  temperature  affect  the  viscosity  or 
mobility  of  water  to  such  an  extent  that  it  moves  more  readily  under 
high  than  low  temperatures.     The  effect  of  temperature  on  capil- 
lary movement   was  shown   on  page  204.    King  found  that  the 
amount  of  water  flowing  through  soil  at  9  degrees  C.  was  6.15 
grams  per  minute,  and  at  32.5  degrees  it  was  10.54  grams.    Briggs 
explained  this  greater  flow  on  the  theory  of  lessened  viscosity,  and 
showed  that  while  the  ratio  between  the  flows  is  1.71,  the  ratio 
between  the  viscosities  is  1.77.     These  correspond  so  closely  thai 
there  is  no  doubt  that  his  conclusion  was  right.     Water  will  perco- 
late through  soils   faster  in   summer  than    winter.     Water  at  32 
degrees  F.  and  at  70  degrees  F.  was  alowed  to  flow  from  a  milli- 
meter opening  under  the  same  pressure  in  each  case.     Twice  as 
much   water  flowed   out  at  70  degrees  as  at  32   degrees.     At  32 
degrees  the  water  did  not  come  out  in  a  stream,  but  dropped  rap- 
idly from  the  tube,  while  at  70  degrees  it  flowed  in  a  steady  stream. 

The  viscosity  is  frequently  affected  by  substances  dissolved  in 
the  soil  water.  Some  substances  increase  while  others  decrease 
viscosity,  as  shown  on  page  20(5.  In  the  case  of  organic  substances 
in  solution  percolation  may  be  aided  by  the  lessened  viscosity. 

5.  Atmospheric   Pressure. — The  changes   in   pressure  of   the 
atmosphere,  with  its  expansion  and  contraction  accompanying  the 
"lows"    and    "highs,"    affect    percolation    to   some    extent.     The 
decrease  of  pressure  allows  the  air  in  the  soil  to  expand,  thus  forcing 
out  some  of  the  water  into  the  drainage  channels.      King-  found 
the  discharge  from  a  spring  to  be  X  per  cent  greater  with  a  falling 
than  a  rising  barometer  and  a  variation  of  15  per  cent  in  the  flow  of 
water  from  a  tile  under  similar  conditions. 

(I.  Shrinkage  Cracks. — The  movement  of  water  by  percolation 
is  aided  greatly  by  the  cracks  that  arc  produced  in  clayev  soils  hv 
shrinkage  during  periods  of  drouth.  These  cracks 'do  not  fully  close 
upon  subsequent  wetting  and  may  thus  leave  passageways  for 
water.  This  is  very  important  in  heavy  soils.  The  burrows  of 
animals,  especially  insects  and  earthworms,  penetrate  the  soil  in 
all  directions  and  furnish  a  ready  means  for  movement  of  water 
both  laterally  and  vertically.  The  greatest  amount  of  work  done 
by  earthworms  is  in  heavy  soils  where  percolation  is  naturallv 
slowest.  These  animals  are  not  abundant  in  acid  soils  and  those 


220 


SOIL  PHYSICS  AND  MANAGEMENT 


deficient  in  organic  matter.  Crayfish  aid  the  downward  movement 
of  water  hy  their  burrows. 

7.  Roots  of  plants  penetrate  the  soil  and  later  decay,  leaving 
passageways  through  which  water  may  pass  quite  readily. 

Lysimeters  or  drain  gages  have  been  used  for  determining  the 
amount  of  percolation  and  evaporation.  The  longest  and  most 
interesting  records  have  been  obtained  at  Rothamsted,  England, 
where  records  have  been  kept  for  34  years.  The  gages  consist  of 
masses  of  undisturbed  soil  of  different  depths  enclosed'  in  cement 
tanks  with  drainage  outlets  for  measuring  the  percolation.  The 
soil  is  a  flinty  clay  loam  or  heavy  loam  and  is  kept  free  from  all 
vegetation. 

Rainfall,  Percolation  and  Evaporation  3  at  Rothamsted,  England,  Average  for 
34  Years,  1871  to  1904 


Months 

Rain- 
fall 

Percolation  through 
soil 

Per  cent  of  rainfall 
percolating  through  soil 

inches 

20 
inches 

40 
inches 

GO 
inches 

20 
inches 

40 
inches 

60 
inches 

January        

2.32 
1.97 
1.83 
1.89 
2.11 
2.36 
2.73 
2.67 
2.52 

1.82 
1.42 
0.87 
0.50 
0.49 
0.63 
0.69 
0.62 
0.88 

2.05 
1.57 
1.02 
0.57 
0.55 
0.65 
0.70 
0.62 
0.83 
1.84 
2.18 
2.15 

1.96 
1.48 
0.95 
0.53 
0.50 
0.62 
0.65 
0.58 
0.76 
1.68 
2.04 
2.04 

78.5 
72.2 
47.6 
26.5 
23.2 
24.0 
25.3 
23.2 
35.0 
57.8 
76.7 
80.3 

88.4 
80.0 
55.6 
30.0 
26.1 
27.6 
25.6 
23.2 
32.8 
57.5 
76.3 
85.4 

84.5 
75.2 
52.0 
28.0 
23.6 
26.3 
23.8 
21.7 
30.0 
52.5 
72.4 
81.0 

February  

March  

April             

May  

June  

July  

August      >   

September  

October  

3.20 
2.86 
2.52 

1.85 
2.11 
2.02 

November  

December  

Total  per  vear  .  . 

28.98 

13.90 

14.73 

13.79 

48.2 

51.0 

48.0 

Results  for  Years  of  Maximum  and  Minimum  Rainfall 


Maximum  (1903)    

38.69 

23.48 

23.60 

24.23 

60.7 

61.0 

63.0 

Minimum  (1898)   

20.49 

7.32 

7.90 

7.69 

35.7 

38.5 

37.6 

It  will  be  noted  from  the  above  table  that  the  amount  of  perco- 
lation varies  but  little  for  the  different  depths  of  soil.  The  average 
percolation  for  tlie  20-inch  deptli  was  13.90  inches,  while  for  the  GO- 
inch  it  was  13.79  inches.  This  shows  that  only  0.11  inch  more  water 
was  retained  by  the  deeper  soil. 


GRAVITATIONAL  WATER 


22  i 


Water  Draining  from  Eight  Fact  of  Saturated  Hands.    Percentage  Based  on  Dry 

Soil,4  King 


Time  of  percolation 

Meshes  per  inch  of  sieves 

20-40 

60-80 

100 

1  hour  

9.6 
13.8 
14.5 
15.3 
16.4 

6.6 
11.8 
12.5 
12.9 
13.6 

1.4 
6.3 
7.5 

8.4 
9.3 

1  day     .        .... 

3  days 

9  days  

268  days  .              

The  table  shows  the  amount  of  water  draining  from  eight  feet 
of  saturated  saml  soil  in  268  days.  The  drainage,  of  course,  was  not 
continuous  during  this  time,  but  varied  with  conditions  of  tem- 
perature and  atmospheric  pressure.  During  the  last  259  days  of 
intermittent  drainage  the  sand  lost  from  6.56  to  9.15  pounds  of 
water  per  square  foot,  or  from  1.2  to  nearly  1.8  inches  of  water. 
Percolation  is  only  possible  when  the  air  can  enter  the  soil,  hence  a 
slight  rain  falling  on  the  surface  may  retard  or  entirely  stop  perco- 
lation by  sealing  the  surface  so  that  the  air  cannot  get  out.  This 
has  been  observed  at  the  Rothamsted  drain  gages. 

QUESTIONS 

1.  Define  gravitational  water. 

2.  W'hat  is  tin1  maximum  water  capacity? 

JJ.   Which  may  have  the  greater  gravitational  water  capacity,  sand  or  clay? 

4.  Define  water  table. 

5.  How  does  the  movement  of  water  through  soil  vary? 

C.  Compare  the  number  of  pores  in  a  sand  soil,  particles  ().().")  mm.,  with  a 
silt  soil,  particles  0.0f>  mm. 

7.  What  about  the  etl'ect  of  shape  and  si/.e  of  particles   in   the  same  soil 

on  percolation  ? 

8.  What  part  does  granulation  play  in  percolation? 
!).  (live  the  effects  of  organic  matter  on   percolation. 

10.  Explain  the  effect  of  viscosity  on  percolation. 

11.  What  things  affect  the  viscosity  of  water? 

12.  Explain   variations  caused    by  changes   in  atmospheric  pressure. 
!.'{.  What  other  factors  aid  percolation? 

14.  Describe  the  Kothamsted  drain  gages. 

15.  What  conclusions  may  be  drawn   from   the   results? 

10.  Give  King's  experiment  regarding  drainage  from   sands. 

REFERENCES 

'King,  F.  If.,  Physics  of  Agriculture.  1007.  p.  134. 
1  King.  V.  H..  The  Soil,  1007,  p.  ISO. 

3  Mall,  A.  1).,  The  Hook  of  the  Kothamstcd  Experiments.  lf)05.  p.  2.'<. 

4  King.   F.   II.,  Wisconsin  Station,    lltli  Ann.   Keport,  p.  28.1. 

General    References — -King.   F.   11..   Principles   and   Conditions  of  the 
Movements  of  Ground  Water.     I".  S.  Geol.  Survey,  19th  Ann.  Report,  Part 

11,  1S07-08,  pp.  (i7-20(i. 


CHAPTER  XVIII 

CONTROL  OF  MOISTURE 
I.  DRAINAGE 

VERY  few  places  on  the  earth's  surface  have  ample  rainfall  so 
well  distributed  that  no  attention  need  he  given  to  the  control  of 
moisture.  In  many  humid  and  superhumid  areas  the  great  prob- 
lem is  disposing  of  the  excess  of  water,  while  in  semi-arid  regions 
it  is  to  conserve  the  rainfall  for  the  crop,  while  in,  the  still  drier 
regions  irrigation  is  the  all-absorbing  problem.  Even  in  the  humid 
areas  some  seasons  are  so  dry  that  the  utmost  care  must  be  exercised 
to  hold  the  moisture  for  the  crop. 

Removal  of  Excess  of  Water. — Drainage. — The  average  soil 
has  about  50  per  cent  of  pore  space.  A  waterlogged  soil  is  one 
having  the  pore  space  filled  with  water.  It  becomes  necessary  to 
remove  this  excess  of  water  so  that  the  food-producing  bacteria 
and  the  roots  of  plants  may  be  able  to  secure  oxygen.  The  water 
table  in  the  soil  must  be  from  three  to  four  feet  below  the  sur- 
face, sufficient  to  give  room  for  the  development  .of  large  root 
systems.  If  it  is  above  this  it  must  be  lowered  by  drainage.  Be- 
sides the  lowering  of  the  water  table  many  other  benefits  are  de- 
rived from  drainage  (Fig.  95). 

(a)  Drainage  gives  stability  to  the  soil.     Ordinarily  when  a 
heavy  weight  is  applied  to  a  very  wet  soil  the  particles  are  pushed 
to  one  side,  the  excess  of  water  weakens  the  cementing  material 
of  the  granules  and  acts  somewhat  as  a  lubricant  to  the  particles. 
This  movement  is  very  injurious  to  the  tilth  of  the  soil,  since  it 
breaks  down  the  granules,  producing  a  puddled  condition.    This  is 
very  likely  to  occur  in  any  soil,  but  more  particularly  in  a  heavy 
one.     Freezing  and  thawing  or  wetting  and  drying  may  overcome 
in  time  the  condition  produced  if  the  soil  is  drained.     Great  dam- 
age is  sometimes  done  by  pasturing  wet  soils  during  late  winter 
and  early  spring. 

(b)  Soils  containing  an   excess  of  water  are  rarely  in  good 
physical  condition.     Granulation  is  produced  by  alternate  wetting 
and  drying,  and  a  soil  that  is  saturated  practically  all  of  the  time 
cannot  be  subjected  to  these  beneficial  conditions.     Freezing  and 

222 


DRAINAGE 


223 


thawing  is  also  another  means  for  producing  granulation,  it'  t lie- 
right  amount  of  water  is  present.  If  there  is  an  excess  of  water  the 
effect  of  freezing  and  thawing  is  to  break  down  the  granules.  In- 
stead of  producing  good  tilth  a  "  runny,"  puddled  condition  results. 
The  soil  of  a  pond  where  water  has  stood  during  the  winter  will 
be  run  together  very  badly  by  spring  and  become  quite  compact. 

(c)  It  seems  almost  paradoxical  that  the  removal  of  the  excess 
of  water  should  increase  the  available  moisture  for  plants,  yet  it  is 
true.  Lowering  the  water  table  to  a  depth  of  three  or  four  feet 
enables  plant  roots  to  develop  in  a  larger  area  than  i*j  otherwise 


Fio.  9.r>. — The  difference  in  germination  and  growth  on  undrained  soil  (Al  and  drained 
(B)  soil.  Same  kind  of  soil  and  the  same  kind  and  number  of  seeds  were  planted,  (t'niversity 
of  Illinois.) 

possible,  since  plant  roots  do  not  penetrate  a  waterlogged  soil. 
This  will  give  them  a  chance  to  secure  the  water  from  a  depth  of 
three  feet  or  more  where  otherwise  they  would  lie  limited  to  one 
or  two  feet.  Capillary  water,  only,  is  used  by  plants,  and  drainage 
increases  the  volume  of  soil  that  contains  this  form  of  moisture. 

(d)  The  removal  of  the  excess  of  water  aids  af ration,  since  the 
water  is  replaced  by  air.  About  50  per  cent  of  the  volume  of  the 
soil  as  it  ordinarily  exists  is  pore  space,  and  about  one-half  of  this 
should  be  occupied  by  air  under  ordinary  conditions.  This,  in  a 
waterlogged  soil,  would  be  filled  with  water.  The  optimum  con- 
dition for  plant  growth  is  sufficient  moisture  for  the  use  of  the 


224 


SOIL  PHYSICS  AND  MANAGEMENT 


plant,  but  not  so  much  as  to  crowd  out  the  oxygen,  which  is 
equally  essential. 

(e)  The  temperature  of  the  soil  will  be  raised  by  the  removal 
of  the  water,  since  the  specific  heat  of  the  soil  will  be  lower  with 
less  water.  If  the  specific  heat  of  water  is  1  and  that  of  soil  is 
0.2,  then  a  waterlogged  soil  having  an  apparent  specific  gravity  of 
1.2  and  50  per  cent  of  moisture  would  have  a  specific  heat  of  0.46, 
or  the  amount  of  heat  required  to  raise  the  temperature  of  the  wet 
soil  one  degree  would  be  more  than  twice  as  great  as  for  the  dry 
soil.  Another  factor  that  affects  the  temperature  is  the  lowering 
of  evaporation  by  drainage.  Evaporation  is  a  cooling  process,  and 
every  pound  of  water  evaporated  from  the  surface  of  the  soil  re- 
quires 966.6  heat  units,  and  this  will  be  taken  largely  from  the 
soil.  Hence  wet  soils  are  "late"  soils.  They  may  be  trans- 
formed into  "  early  '*  ones  by  drainage  (Fig.  95). 

Drainage  lengthens  the  growing  season  of  certain  soils,  and 
may  possibly  permit  a  complete  change  of  crops.  Conditions  are 
more  favorable  for  biological  activity  in  the  drained  soil  because 
of  the  increase  in  temperature  and  of  better  aeration.  King  found 
that  well-drained  sandy  loam  had  a  temperature  of  66.5  degrees  F., 
while  in  an  undrained  black  marsh  the  temperature  was  54  degrees 
at  the  same  depth. 

Experiments  conducted  with  trays  filled  with  the  same  soil, 
one  of  which  was  drained  while  the  other  was  not,  show  differences 
as  given  in  the  table. 

Effect  of  Drainage  on  Temperature  of  a  Soil l — Degrees  Fahrenheit 


Thermometer  1  inch 

Thermometer  2  inches 

Thermometer  4  inches 

Time 

below  surface 

below  surface 

below  surface 

Drained 

Undrained 

Drained 

Undrained 

Drained 

Undrained 

6  A.M. 

46.7 

45.0 

49.0 

47.2 

52.5 

50.0 

8  A.M. 

58.0 

52.5 

53.0 

50.5 

51.0     ' 

49.5 

10  A.M. 

75,0 

67.0 

66.5 

61.0 

57.5 

54.0 

12  M. 

85.5 

73.5 

77.0 

68.5 

67.0 

62.0 

1  P.M. 

87.5 

73.8 

79.4 

70.7 

70.6 

65.1 

2  P.M. 

84.0 

72.0 

81.0 

72.0 

74.2 

68.0 

3  P.M. 

81.0 

70.0 

80.0 

71.0 

76.5 

70.5 

4  P.M. 

76.1 

65.1 

77.0 

68.5 

76.8 

70.8 

5  P.M. 

71.2 

63.8 

74.2 

66.3 

75.4 

70.0 

6P.M. 

68.0 

62.0 

72.1 

65.0 

74.0 

69.0 

i 

It  will  be  noted  that  the  greatest  difference  between  the  drained 
and  undrained  soil  at  one  inch  in  depth  was  13.7  degrees,  at  two 
inches  9  degrees,  and  at  4  inches  6.2  degrees. 


DRAINAGE 


225 


(f)  The  removal  of  the  excess  of  water  from  the  soil  increases 
decomposition  and  nitrification,  processes  necessary  for  the  growth 
of  plants.     As  a  general  rule,  the  mosses  and  grasses  of  swamps 
have  decomposed  to  a  very  slight  extent  only,  because  of  the  excess 
of  moisture  which  prevents  the  access  of  oxygen.     Drainage  allows 
aeration  and  the  process  of  nitrification  may  then  take  place. 

(g)  "Heaving"  of  soil  or  crops  on  medium-  to  fine-grained 
soils  is  diminished   or  almost  entirely  prevented  l>y  the  removal 
of  the  water.     When  a  wet  soil  freezes  it  expands  in  the  direction 
of  least  resistance,  which  is  upward,  and  the  crop,  whatever  it  is, 


Fro.   9R. — Pipe  heaved  nearly  0  inches  during  winter  of  lOl.S-lOlfi. 

is  pushed  along  with  it.  This  process  heing  repeated  over  and 
over  may  "  heave"  a  crop  out  of  the  soil  entirely,  as  in  the  ease  of 
young  alfalfa,  clover  or  wheat.  If  the  soil  is  drained,  the  expan- 
sion of  the  smaller  amount  of  water  in  free/ing  will  lie  taken  care 
of  in  the  pore  spaces  of  the  soil  without  expanding  upward  to 
such  great  extent.  Figure  !><;  shows  the  heaving  of  a  gas  pipe 
stake  during  one  winter,  and  figure  !)?  shows  the  heaving  of 
alfalfa  in  a  poorly  drained  soil.  Where  tight  suhsoils  are  present 
the  danger  of  heaving  is  very  great,  so  that  it  is  praeticallv  im- 
possihle  to  grow  alfalfa  and  clover. 
15 


226  SOIL  PHYSICS  AND  MANAGEMENT 

(h)  The  effectiveness  of  thorough  drainage  in  preventing 
erosion  has  heen  ohserved  in  many  instances,  but  this  point  is  dis- 
cussed under  the  subject  of  erosion. 

(i)  Drainage  is  one  of  the  most  effective  means  for  removing 
alkali  from  land  under  irrigation,  and  thus  preventing  its  "  rise '' 
and  consequent  injury  to  crops.  It,  in  conjunction  with  flooding, 
is  also  an  effective  method  for  reclaiming  land  that  contains  so  much 
alkali  as  to  render  it  unproductive. 

Types  of  Drainage. — Two  general  types  of  drainage  have  been 
employed,  open  and  tile  drains. 

(a)  Open  Drains. — In  a  great  many  cases,  the  open  drain  is 
an  absolute  necessity,  because  the  large  amount  of  water  to  be 
carried  off  precludes  the  possibility  of  using  covered  drains  at  a 
reasonable  cost.  Hence  there  will  always  be  a  large  number  of 


Fio    97  — Alfalfa  that  was  completely  killed  by  heaving.     Note  roots  'lying  on  surface. 

(S.  V.  Holt.) 

open  drains,  such  as  dredge  ditches.  In  some  cases  open  ditches 
are  necessary  because  quicksand  is  present  which  enters  the  drains 
through  the  openings  between  -the  tiles  and.  fills  them  so  as  to  re- 
duce their  efficiency  or  even  clog  them  entirely.  In  other  places 
the  fall  or  slope  of  the  land  is  so  slight  that  tile  drains  would  be 
of  very  little  use  and  hence  the  open  ditch  becomes  a  necessity. 

A  form  of  open  or  surface  drainage  that  is  effective  and  adapted 
to  certain  types  of  soil  is  that  practiced  on  soils  with  hardpan  or 
tight  clay  substrata.  Such  soils  occur  in  various  parts  of  the 
country  and  the  form  of  drainage  adapted  to  them  is  that  of  dead 
furrows  or  shallow  ditches  about  20  or  25  feet  apart.  These  are 
employed  to  a  large  extent  on  areas  with  tight  clay  subsoils. 

There  are  several  serious  objections  to  open  drains.  They  aie 
almost  invariably  expensive  forms,  because  constant  care  is  needed 


DRAINAGE 


227 


to  keep  the  ditches  open  and  in  good  condition  (Figs.  98,  OS),  100). 
In  a  few  years  the  fall  may  become  very  uneven,  due  to  more  rapid 
erosion,  at  one  place  than  at  another.  Obstructions  may  get  into 


FIG.  98 


FIG.  99 


FIG.   98. — The  obstructions  interfere  with  the  current  and  cause  deflections.     (H.  C. Wheeler.) 
Flo.  99. — Ditch   gradually   being    filled   by   soil   due   to  current  being    retarded  by   grass. 

(C.  C.  Comstock.) 


Fio.    100. — A  neglected  ditch  often  soon  in  heavily  wooded  ureas.      (.11.  C    Wheeler.) 

the  ditch  which  will  cause  deflection?  of  the  current  and  result  in 
wearing  away  of  the  hank.  There  is  always  a  considerable  waste 
of  land  in  connection  witli  open  drains  even  at  the  verv  best,  and 


228 


an  open  ditch  is  always  in  the  way.  It  interferes  very  seriously  in 
many  cases  with  tillage  of  laud,  but  one  of  the  most  serious  ob- 
jections is  the  lack  of  physical  benefit  to  the  soil  from  open  ditches 
in  comparison  with  tile  drains. '  This  is  principally  due  to  the 
fact  that  small  open  drains  are  never  as  deep  as  the  corresponding 
tile  drain  and  do  not  remove  the  water  as  completely.  The  growth 
of  weeds  and  grass  clogs  the  ditch  and  renders  it  less  effective. 

(b)  Tile  Drains. — Since  the  object  of  drainage  is  to  lower  the 
water  table,  the  tile  should  be  amply  large  and  the  lines  sufficiently 
close  together  and  at  such  depth  that  the  water  may  be  removed 
before  the  crop  suffers  serious  injury.  If  the  tile  is  laid  deep 
enough  to  lower  the  water  table  to  only  two  feet  beneath  the  sur- 
face on  an  average,  a  rain  of  two  or  three  inches  will  raise  it  in- 
juriously near  the  surface,  and  if  frequent  rains  follow  the  crop 
will  be  damaged  in  spite  of  the  fact  that  the  land  is  tiled.  If 
the  tile  is  too  small  this  slow  removal  may  permit  very  serious 

of  Soil 


/  2 

FIG.  101.— Showing  the  water  table  at  a,  with  lines  of  tile  at  1  and  3,  and  at  bb,  soon 
after  the  insertion  of  another  line  at  2  and  later  at  b'b'.  The  slope  of  the  water  table  between 
the  lines  of  tile  varies  with  the  perviousness  of  the  soil. 

injury.  If  the  water  table  is  three  feet  beneath  the  surface  and 
the  foot  of  soil  above  it  is  two-thirds  saturated,  a  rainfall  of  two 
inches  will  raise  the  water  table  a  foot  at  least  and  damage  to  the 
crop  may  result. 

The  topography  of  the  water  table  in  tile-drained  land  consists 
of  a  series  of  ridges,  with  the  crests  about  midway  between  the 
lines  of  tile.  The  height  of  these  crests  above  the  tile  depends  upon 
the  texture  and  character  of  the  soil  strata,  the  distance  between 
the  lines  of  tile  and  the  amount  of  rainfall  (Fig.  101).  In  laying 
tile  the  character  of  the  soil  should  be  taken  into  account  and  the 
lines  placed  close  enough  together  so  that  the  water  table  will  be 
lowered  to  at  least  30  inches  beneath  the  surface  at  its  highest 
point.  It  must  be  remembered  that  the  most  of  the  water  does  not 
simply  pass  downward  into  the  tile,  but  it  must  move  laterally 
from  two  to  five  rods,  depending  upon  the  distance  between  the 
lines.  The  lateral  movement  is  comparatively  slow,  so  much  so  in 


DRAINAGE  229 

many  soils  that  the  crop  is  frequently  damaged  lie  fore  the  water 
table  is  lowered  beyond  the  point  of  injury.  The  lines  of  tile 
should  be  laid  closer  in  somewhat  impervious  soils  than  in  pervious 
ones.  In  tight  clay  subsoils  the  tile  drains  should  be  not  over  four 
rods  apart,  and  no  doubt  two  rods  would  be  better. 

Coarse-textured  soils  generally  drain  better  than  fine  ones.  An 
occasional  tight  stratum  only  a  few  inches  thick  may  seriously  in- 
terfere with  drainage.  In  general,  limestone  soils  drain  better 
than  strongly  acid  ones  because  of  the  granulation  produced  by  the 
limestone.  Heavy  soils  are  especially  aided  by  shrinkage  and  the 
formation  of  cracks  to  a  depth  of  several  feet  which  may  not  com- 
pletely close.  Earthworms,  crayfish  and  other  animals  do  much 
to  open  up  the  soil  for  free  movement  of  water,  both  laterally  and 
vertically. 

QUESTIONS 

1.  What  problems  come  up  in  the  control  of  moisture? 

2.  Define  a  waterlogged  soil.      What  objections  to   it? 

3.  Explain  some  of  the  results  of  lack  of  stability   in  a  soil. 

4.  Why  are  permanently  saturated  soils  usually  in  poor  tilth? 

5.  How  does  drainage  affect  the  available  moisture? 
0.  Explain  how  aeration  is  affected  by  drainage. 

7.  What  is  the  effect  of  drainage  on  the  specific  heat  of  a  soil  ?     Why? 

8.  Why  does  drainage  affect  evaporation  ? 

!).  How  may  drainage  affect  crops  and  the  length   of  growing  siason? 

10.  Why  are  decomposition  and  nitrification  necessary? 

11.  How  does  drainage  prevent  heaving? 

12.  Why  does  a  tight  subsoil  cause  heaving? 
1.'5.  Why  are  open  drains  necessary? 

14.  How  are  tight  clay  soils  usually  drained? 

15.  What  are  some  objections  to  open  ditches? 

l(i.  What  precautions  should  be  observed  in  tiling?     Why? 

17.  Upon  what  does  the  topography  of  the  water  table  depend? 

18.  How  low  should  the  water  table  be? 

10.  Why  is  lateral  movement  of  water  through  soils  so  slow? 

20.  What  are  some  of  the  soil  conditions  that  aid  drainage? 

REFERENCE 

1  Unpublished  data,  University  of  Illinois. 

General  References. — Whitson,  A.  K..  and  Jones.  E.  R..  Bulletin  140, 
Wisconsin  Station,  Drainage  Conditions  in  Wisconsin,  1007.  Kippin,  E.  ()., 
Bulletin  2.14.  Cornell  Station.  Drainage  in  New  York.  I'.tOS.  .Fetfery.  J.  A., 
Bulletin  50  (special),  Michigan  Station,  Tile  Drainage.  1011.  Smith,  A. 
(}.,  Farmers'  Bulletin  524.  U.  S.  I).  A..  The  Drainage  of  the  Farm.  1013. 
Yarnell.  D.  T,.,  Farmers'  Bulletin  (>OS.  I'.  S.  1).  A..  Trenching  Machinery 
for  Tile  Drains,  1015.  Hills.  .1.  T,..  .Tones.  C.  II..  Williamson,  C.  (I.,  and 
Burdick,  K.  T.,  Bulletin  17.'?.  Vermont  Station.  Principles  of  Land  Drain 
age,  1013.  Woodward.  S.  M..  Bulletin  30».  T*.  S.  D.  A..  Land  Drainage  by 
"Means  of  rumps.  1015.  Elliot.  C.  C...  Farmers'  Bulletin  1S7.  T'.  S.  D.  A'.. 
Drainage  of  Farm  Lands.  1004.  Kincr.  F.  H..  Irrigation  and  Drainage. 
Part  II,  Revised  Ed.,  1000.  Jcffery,  J.  A.,  Land  Drainage.  lOlfi. 


CHAPTER    XIX 

CONTROL  OF  MOISTURE 

II.  TILLAGE 

ONE  of  the  means  for  controlling  moisture  that  is  quite  uni- 
versally practiced  is  that  of  tillage.  It  finds  application  in  arid  and 
semi-arid  sections  at  all  times  and  in  humid  and  superhumid 
regions,  more  particularly  in  periods  of  drouth.  Any  form  of 
implement  that  stirs  the  soil,  from  the  crudest  form  of  hoe  to 
the  powerful  tractor  with  its  dozen  plows  and  its  harrows,  will 
accomplish  the  same  ohject. 

Increasing  the  Moisture  Capacity  of  Soils. — Probably  one  of 
the  most  important  factors  in  supplying  soils  with  sufficient  moist- 
ure for  crops  is  by  increasing  their  water  holding  capacity.  This 
may  be  accomplished  by  several  methods: 

(a)  By  Tillage. — 'Soils  frequently  become  so  compact  that  they 
will  not  absorb  water  readily,  hence  there  will  be  a  large  run-off 
and  a  consequent  loss  not  only  of  water  but  of  soil  material  due 
to  erosion.     Only  the  water  that  is  absorbed  can  be  of  any  benefit 

i  to  crops.  Hence  it  becomes  very  necessary  to  put  the  soil  in 
condition  to  absorb  as  much  water  as  possible.  This  can  best  be 
accomplished  by  stirring  the  soil  to  considerable  depth  with  some 
form  of  plow.  The  best  implement  for  this  purpose  is  the  com- 
mon mold  board  plow.  In  plowing,  the  soil  is  not  only  inverted, 
but  pulverized,  and  this  is  very  beneficial  if  the  soil  is  in  proper 
condition  with  respect  to  moisture.  To  increase  the  storage  capacity 
to  the  greatest  extent  plowing  should  be  as  deep  as  possible.  The 
storage  capacity  may  easily  be  doubled  by  this  means  and  the  soil 
put  in  condition  to  absorb  water  readily  so  that  very  little  runs  off. 
This  practice  is  especially  advisable  on  rolling  land  and  in  semi- 
arid  regions. 

(b)  Compacting  the  Soil. — In  the  process  of  plowing  the  soil 
is  left  too  loose  for  retaining  moisture  to  the  highest  degree,  either 
against  percolation  or  evaporation, 'and  in  order  to  bring  about 
proper  conditions  a  certain  amount   of  compacting  is  necessary. 
This  may  be  done  by  various  implements,  such  as  the  spike-tooth 
harrow,  the  disk  harrow,  the  rotary  harrow,  the  corrugated  roller, 

230 


TILLAGE  231 

or  the  subsurface  packer.  The  use  of  these  implements  closes  any 
large  air  spaces  that  exist  in  the  soil  that  would  tend  to  increase 
either  evaporation  or  percolation  and  hence  renders  the  soil  much 
more  retentive  of  moisture  than  it  would  he  otherwise. 

(c)  Organic  Matter. — The  water  holding  capacity  of  the  soil 
may  he  largely  increased  through  the  addition  of  organic  matter. 
This  constituent  acts  as  a  sponge,   absorbing  large  quantities  of 
water   which    are    held   against    the   force   of   gravity.      Capillary 
movement  is  retarded,  thus  decreasing  surface  evaporation. 

(d)  Deep  Rooting  Crops. — The  effect  of  deep  rooting  crops 
is  somewhat  similar  to  deep  plowing  or  subsoiling  except  that  the 
openings   made   by    the    roots   become   partly    filled   with   organic 
matter,    which   in   itself    is   beneficial.      The    openings    furnish    a 
passageway  for  water  and  air  to  greater  depths  than  any  practical 
tillage  could  do,  thus  enlarging  the  water  reservoir.     The  decay  of 
the  organic  matter  produces  a  somewhat  granular  condition  in  the 
deeper  subsoil  that  aids  in  the  absorption  and  retention  of  moisture. 
Often  the  subsurface  and  subsoil  become  so  compact  that  the  water 
is  prevented  from  percolating  through  them  to  any  great  extent, 
and  this  permits  the  surface  stratum  to  become  saturated  and  then 
a  large  amount  of  run-off  and  evaporation  must  necessarily  occur. 

Removing  the  Excess  of  Moisture  by  Tillage. — The  re- 
moval of  water  by  tillage  is  not  often  practiced  and  its  applica- 
tion is  very  limited.  Yet  if  a  few  inches  of  surface  soil  con- 
tains too  much  water  this  may  be  removed  to  some  extent  by 
tillage,  which  encourages  evaporation  from  the  stirred  soil,  but 
the  greatest  care  is  necessary.  The  soil  may  be  plowed  or  culti- 
vated and  left  somewhat  rough,  thus  giving  it  a  chance  to  dry 
out.  This  may  purmit  seeding  earlier  than  if  left  in  its  orig- 
inal compact  condition.  In  certain  soils  rolling  may  be  of  benefit 
because  of  the  effect  it  has  in  compacting  the  soil  and  facilitating 
capillary  movement  of  moisture  to  the  surface  where  it  is  evapo- 
rated. Frequent  cultivation  may  also  have  a  similar  effect  in 
drying  out  the  cultivated  soil,  since  every  cultivation  will  bring  to 
the  surface  moist  soil  that  will  become  dry.  and  better  conditions 
for  seeding  may  be  produced  in  this  way.  This  should  not  be 
practiced  with  soils  that  are  easily  puddled,  but  may  be  advisable 
for  sandy  soils  or  those  having  an  abundance  of  organic  matter. 

Decreasing  Losses  from  Soils. — Water  is  lost  from  soils 
by  percolation  to  depths  below  fhe  capillary  limit  by  drainage  or 


232  SOIL  PHYSICS  AND  MANAGEMENT 

percolation,  by  transpiration  from  leaves  of  plants  and  by  evapora- 
tion from  the  surface  of  the  soil. 

(a)  Decreasing  Percolation. — The  amount  of  percolation  de- 
pends very  largely  on  the  texture  of  the  soil  itself.     As  a  general 
rule,  the  coarser  the  texture  or  the  larger  the  air  spaces  the  greater 
the  amount  of  percolation.     This,  of  course,  may  be  modified  by 
the  amount  of  compaction  and  also  by  the  organic-matter  content. 
The  amount  of  percolation  depends,  too,  on  the  openness  of  the 
soil  produced  by  tillage   as  given   above.     Excessive  percolation 
where  it  is  due  to  coarseness  of  soil  texture  is  very  difficult  to 
prevent. 

The  incorporation  of  some  water-retaining  material  such  as 
clay  or  any  of  the  finer  soil  constituents  or  organic  matter  with 
the  sand  or  gravel  will  aid  in  accomplishing  the  results  desired. 
The  former  is  an  expensive  process,  but  has  been  done  on  a  small 
scale  with  excellent  results.  The  use  of  organic  matter  is  a 
more  practical  but  somewhat  slower  process  unless  under  condi- 
tions where  abundant  supplies  of  farm  manure  are  at  hand.  Com- 
pacting is  very  beneficial  in  case  of  sandy  soils,  but  must  be  care- 
fully done  in  the  case  of  heavy  soils. 

(b)  Decreasing  Transpiration  from  Plants. — All  plants  in 
their  growth  require  enormous  amounts  of  water,  practically  all 
of  which  must  be  secured  from  the  soil.     We  have  seen  that  from 
300  to  500  pounds  of  water  are  required  for  each  pound  of  dry 
matter  produced.     This  means  that  crops  remove  large  quantities 
of  water  from  the  soil. 

The  relative  amount  of  water  required  may  be  reduced  by  an 
abundance  of  plant  food  provided  through  cultivation,  rotation 
and  fertilization.  Weeds  and  other  plants  foreign  to  the  crop 
should  be  destroyed  to  prevent  them  from  depriving  it  of  the 
moisture  necessary  for  its  growth. 

(c)  Preventing  Evaporation  by  Mulches. — A  mulch  is  any 
material  placed  on  or  produced  from  the  surface  soil  by  tillage. 
Its  object  is  to  prevent  evaporation.    To  be  effective  a  mulch  must 
be  dry.     Since  moisture  films  pass  very  slowly  into  dry,  loose  soil, 
practically  all  of  the  moisture  that  is  lost  is  by  interstitial  evapo- 
ration and  diffusion  through  the  mulch  air  to  the  atmosphere  above. 
This  diffusion  takes  place  very  slowly. 

The  following  table  gives  the  results  obtained  by  Buckingham 


TILLAGE 


233 


with  different  depths  of  air-dry  mulches,  the  soil  used  being  the 
Leonardtown  loam: 

Loss  of  Water  by  Interstitial  Evaporation,    and  Diffusion  Through  Mulches  of 
Varied  Thickness  of  Leonardtown  Loam  1 


Depth  of  mulch 

Moisture  lost 
per  year 

inches 

i«c/its 

1 

2.71 

2 

1.60 

b 

Depth  of  mulch 

Moisture  lost 
per  year 

inches 

inches 

4 

0.95 

6 

0.09 

With  a  1^-inch  mulch  of  Takonia  lawn  soil  the  loss  of  moisture 
amounted  to  one  inch  in  six  years.  The  amounts  lost  are  so 
small  that  they  need  not  he  taken  into  account.  I  nder  field  con- 
ditions a  mulch  is  rarely  ever  perfect.  There  will  he  some  places 
where  capillarity  is  at  work.  Hence  under  Held  conditions  labora- 
tory results  are  seldom  attained,  hut  they  furnish  principles  to 
guide  in  farm  practice.  All  mulches  enclose  air  of  high  humidity, 
thus  retarding  or  preventing  evaporation  from  the  moist  soil  be- 
neath. The  dry  layer  prevents  capillary  movement  to  the  surface 
and  is  made  much  more  effective  by  its  looseness. 

There  are  two  kinds  of  mulches,  artificial  and  soil  mulches. 

(a)  Artificial    mulches    are    formed    by    the    application    of 
manure,   straw,   chaff,   peat,   leaves,   sawdust  and    other   materials 
to  prevent  evaporation.     This  method  must  necessarily  be  very  lim- 
ited in  its  application  because  of  the  expense  attached  and  labor 
involved.     Such  mulches  are,  however,  very  effective.     At  the  same 
time  other  objects  are  accomplished,  such  as  preventing  the  growth 
of  weeds  and  adding  plant  food.     Strawberries  and  bush  fruits  are 
sometimes  mulched  with  straw,  manure  or  leaves.     "'  Straw"  pota- 
toes are  grown  quite  extensively  on  the  deep  loessial  soils  along  the 
Mississippi   river.     The  potatoes  are  planted   three  or   four  inches 
deep   in    the  soil.      After  the   soil    becomes   warm   and    before   the 
potatoes  come  up  they  are  covered  with  straw  to  a  depth  of  six  or 
eight   inches.      It    keeps   down    the    weeds,   conserves   moisture  and 
furnishes  some  plant  food  which  is  leached  <  ut  of  the  straw  into  the 
soil. 

In  jMirope  and  other  countries  stones  are  placed  upon  the  sur- 
face of  the  soil  in  hillside  vineyards  to  conserve  the  moisture. 
Gravel  is  sometimes  applied  for  the  same  purpose. 

(b)  Soil  mulches  are  by   far  tin1  most   practical  and  common 
means  of  conserving  moisture.     They  are  applicable  to  all  climates 


234 


SOIL  PHYSICS  AND  MANAGEMENT 


and  conditions.  The  soil  mulch  consists  of  a  dry  layer  of  soil, 
either  loose  or  compact.  The  loose  mulch  is  far  more  effective  and 
common  than  the  compact  (Fig.  102).  This  latter  results  only 
after  much  moisture  has  been  lost  from  the  soil,  and  should  not  be 
depended  upon. 

Some  soils  are  self  mulching  to  a  certain  extent.  Sands,  peats 
and  highly  granular  soils  are  of  this  character.  The  best  way  of 
producing  a  soil  mulch  is  by  tillage,  the  kind  of  implement  depend- 
ing upon  the  soil,  its  tilth  and  moisture  content,  and  the  kind  and 
condition  of  the  crop. 

Fineness  of  the  Mulch. — Mulches  may  be  made  too  fine  to  he 
of  greatest  value  under  all  conditions.  If  fine-  or  medium-grained 

' 


FIG.   102. — A  good  method  of  conserving  moisture. 

soils  contain  little  organic  matter,  cultivation  tends  to  produce  a 
mulch  of  individual  particles  or  a  dust  mulch,  which,  while  it  serves 
very  well  for  preventing  evaporation,  yet  serves  equally  well  for 
preventing  absorption  of  rainfall.  Hence  the  first  dash  of  a  heavy 
shower  causes  these  particles  to  run  together  and  produce  an  almost 
impervious  stratum.  If  the  mulch  is  not  so  fine  or  is  somewhat 
cloddy  or  granular  this  running  together  does  not  take  place  so 
readily  and  a  much  larger  proportion  of  the  rainfall  will  be  ab- 
sorbed. This  in  arid  regions  becomes  a  very  serious  problem  where 
it  is  desirable  that  all  of  the  rainfall  should  be  absorbed.  Hence 
a  mulch  should  not  be  made  with  an  implement  that  reduces  the 
soil  to  dust. 


TILLAGE 


235 


The  Depth  of  the  Mulch. — The  deeper  the  mulch  the  more 
effective  it  is.  King  has  shown  very  conclusively  that  evaporation 
is  prevented  to  a  very  large  extent  by  deeper  mulches.  The  fol- 
lowing table  gives  his  results : 


Effectiveness  of  Soil  Mulches  of  Different  Kinds  and  Depth 

100  Days 


-Water  Loxt  in 


No  mulch 

Mulch 
1  inch 
deep 

Mulch 
2  inches 
deep 

Mulch 
3  inches 
deep 

Mulch 
4  inches 
deep 

Black  marsh  soil: 
Tons  per  acre  .... 
Inches  of  water.  .  . 
Per  cent  saved  by 
mulches 

588.0 
5.193 

355.0 
3.12 

34.54 

270.0 
2.384 

54.08 

256.4 
2.265 

56.39 

252.5 
2.230 

57.06 

Sandy  loam  : 
Tons  per  acre  . 
Inches  of  water 
Per  cent  saved 
by  mulches 

741.5 
6.548 

373.7 
3.3 

49.69 

339.3 
2.996 

54.24 

287.5 
2.539 

61.22 

315.4 
2.785 

57.47 

Virgin  clay  loam  . 
Tons  per  acre  .  . 
Inches  of  water 
Per  cent  saved 
by  mulches.  . 

2,414 
21.31 

1,260 
11.13 

47.76 

979.7 
8.652 

59.38 

889.2 
7.852 

63.13 

883.9 
7.805 

63.34 

It  will  be  noted  from  this  table  that  the  four-inch  mulch  was 
no  more  effective  than  the  three-inch. 

Deep  mulches  are  very  effective  in  conserving  moisture,  but 
there  are  serious  objections  to  their  use  where  crops  are  grow- 
ing. The  objections  apply  more  directly  to  farming  in  humid 
than  in  semi-arid  and  arid  regions.  If  in  humid  areas  a  mulch 
three  or  four  inches  deep  is  produced  on  a  sail  with  an  intertilled 
crop,  serious  root  injury  will  occur  which  will  materially  decrease 
yields.  Deep  mulches  are  practical  only  on  bare  soils.  The  effec- 
tiveness of  a  mulch  depends  upon  its  looseness  and  drynoss.  A 
three-inch  mulch  means  the  loss  of  a  large  amount  of  water  if  it 
is  to  be  effective  to  its  full  depth.  To  maintain  a  mulch  of  this 
depth  more  frequent  cultivation  is  necessary  than  for  shallow 
.ones.  Every  cultivation  turns  under  dry  soil  and  brings  moist  soil 
to  the  surface,  resulting  in  loss  of  moisture.  Shallow  mulches  are 
easily  maintained  with  a  minimum  of  cultivation.  Tn  humid 
climates,  if  the  crop  is  free  from  weeds,  there  is  little  necessity  for 
cultivation  of  sands,  sandy  loams  and  silt  lo;uns. 

Besides  the  moisture  lost  from  the  mulch  the  plant  food  that 


236  SOIL  PHYSICS  AND  MANAGEMENT 

it  contains  is  unavailable  for  the  use  of  the  crop.  If  the  mulch  is 
three  inches  deep  it  means  that  about  one-half  of  the  plowed  soil, 
the  most  fertile  part,  has  little  value  except  for  the  conservation 
of  moisture,  and  in  humid  climates  this  layer  is  of  much  greater 
value  to  the  crop  for  the  plant  food  it  contains  than  for  the  moisture 
it  conserves. 

Maintenance  of  the  Mulch. — Under  certain  conditions  the 
soil  mulch  may  be  entirely  destroyed  or  rendered  much  less  effec- 
tive by  a  shower,  so  that  it  becomes  necessary  to  renew  it.  Tillage 
of  some  kind  must  be  resorted  to  in  order  to  reproduce  it.  After  a 
light  shower  a  harrow  or  weeder  may  be  effective  in  renewing  it. 

The  ease  with  which  a  mulch  may  be  maintained  depends  to  a 
large  extent  upon  the  kind  of  soil.  Sands  and  sandy  loams  respond 
readily  to  tillage  and  the  mulch  is  easy  to  produce.  Soils  contain- 
ing large  amounts  of  organic  matter  are  granular,  and  a  loose, 
mellow  surface  mulch  is  maintained  without  difficulty.  Heavy 
soils,  low  in  organic  matter,  present  the  greatest  difficulty,  since 
they  are  likely  to  be  cloddy  and  deficient  in  granulation.  To  pro- 
duce a  good  mulch  in  these  soils  by  mechanical  means  alone  is 
almost  impossible.  Anything  that  encourages  flocculation  will 
materially  aid  in  the  formation  of  mulches. 

The  maintenance  of  a  mulch  is  especially  important  in  arid 
and  semi-arid  sections  where  so  much  depends  upon  the  conserva- 
tion of  moisture.  Even  with  small  grain  the  mulch  is  maintained 
by  means  of  a  light  spike-tooth  harrow  or  weeder  until  the  grain 
by  shading  the  soil  prevents  excessive  evaporation. 

QUESTIONS 

1.  What  effect  does  compacting  have? 

2.  What  form   of  tillage  increases  the  moisture  capacity  of  soils  to  the 

greatest  degree? 

3.  TTow  does  organic  matter  affect  the  water-holding  capacity  of  soils? 

4.  Explain  the  effect  of  deep  rooting  crops  on  water  capacity  of  soils. 

5.  How  may  water  be  removed  by  tillage? 

6.  How  may  excessive  percolation  be  overcome  or  prevented  ? 

7.  Explain  how  transpiration  may  be  reduced. 

8.  How  much  moisture  is   lost  by   interstitial  evaporation  and   diffusion 

through  the  mulch  ? 

9.  Why  is  it  impossible  to  have  a  perfect  mulch  under  field  conditions? 

10.  How  does  the  humid  soil  air  of  the  mulch  prevent  evaporation? 

11.  Define  an  artificial  mulch. 

12.  Give  advantages  and  disadvantages  of  its  use. 

13.  What  is  a  soil  mulch? 

14.  How  is  it  effective  in  retaining  moisture? 


TILLAGE  237 

15.  Give  facts  regarding  fineness  of  mulches. 

10.  What  conclusion  may  be  drawn  from  King's  work  as  given  in  table  on 
page  23o? 

17.  What  are  some  disadvantages  of  a  three-inch  mulch? 

18.  How  deep  should  the  mulch  be? 

19.  How  does  a  shower  destroy  a  mulch? 

20.  What  part  does  texture  play  in  the  ease  with  which  a  mulch  may  be 

maintained? 

21.  How  often  should  cultivation  be  done  to  maintain  a  mulch? 


REFERENCES 

'Buckingham,  E.,  Bulletin  38,  Bureau  of  Soils,  U.  S.  D.  A.,  Studies  in  the 

Movement  of  Soil  Moisture,  1!K)7,  p.  17. 
•King,  F.  1L,  Physics  of  Agriculture,  11)07,  p.  180. 


CHAPTER    XX 

CONTROL  OF  MOISTURE 
III.  DRY-LAND  AGRICULTURE 

THE  distribution  of  rainfall  over  the  surface  of  the  earth  is  very 
irregular,  so  that  extensive  areas  are  deficient  in  moisture  and 
special  cultural  methods  and  special  crops  must  be  used.  Many 
regions  are  so  poorly  supplied  with  moisture  that  crops  cannot  be 
grown,  even  under  the  best  conditions,  without  irrigation.  It  will 
be  well  to  consult  the  table,  page  189,  on  the  annual  precipitation 
on  the  earth's  land  surface.  The  map,  figure  89,  may  be  of  further 
help  in  giving  a  correct  idea  as  to  the  location  of  the  humid  and 
dry  areas. 

From  the  table,  page  189,  it  is  seen  that  approximately  65  per 
cent  of  the  land  area  of  the  earth  receives  less  than  30  inches  of 
rainfall.  About  25  per  cent  receives  less  than  10  inches,  while  40 
per  cent  has  from  10  to  30  inches.  In  the  United  States  alone  the 
dry-land  region  covers  about  one-half  the  entire  area,  and  1,135,000 
square  miles  of  this  is  suitable  for  dry  farming.  Australia  has 
about  the  same  amount,  and  extensive  areas  are  found  in  Africa 
and  Asia  and  smaller  ones  in  Europe  and  South  America. 

Adaptation  of  a  Region  to  Dry  Farming. — In  dry-land 
farming,  while  the  amount  of  moisture  supplied  by  the  rainfall 
is  by  far  the  most  important  factor,  yet  there  are  secondary 
ones«4hat  must  be  taken  into  consideration.  These  are  frequently 
of  sufficient  importance  to  bring  absolute  failure  if  overlooked  or 
neglected.  These  include  evaporation  and  the  character  of  the 
soil,  which  are  of  almost  equal  significance  with  the  rainfall. 

(a)  Rainfall. — The  adaptation  of  a  region  to  dry  farming  de- 
pends upon  several  factors,  one  of  the  principal  ones  being  the 
amount  of  rainfall  and  its  distribution  through  the  year  (Pig. 
103).  Dry  farming  is  not  practical  with  less  than  10  inches  of 
rainfall  annually,  but  there  are  modifying  factors.  With  this 
amount  the  moisture  must  be  carefully  stored  and  conserved  for 
the  crops.  The  margin  is  so  narrow  that  a  year  or  two  with  a 
238 


DRY-LAND  AGRICULTURE 


239 


rainfall  but  slightly  below  the  normal  will  result  in  failure.     The 
distribution  of  this  rainfall  is  quite  important,  although  not  so 


AW70SA  TYPE 


AROOCVMIJiKI  HII131 


PlAINSTVre 


uunmi        irninuiiirviii 


.urn.,  im.,1  nil 


Fio.  103.— Typ«a  of  rainfall  over  the  dry-farm  area  ,of  the  United  States.     (AfUr  Henry) 


Fio.   104. — Sngp  bnish  on  land  woll  adnptod  to  dry  farming.     I'tan. 

much  so  as  in  Inimid  regions,  since  l>y  practicing  llio  best  methods 
of  conservation  the  moisture  may  lie  held  in  the  soil.  It  is,  how- 
ever, desirable  to  have  the  rainfall  during  the  growing  season. 


240 


SOIL  PHYSICS  AND  MANAGEMENT 


FIG.    105. — A  gravelly  soil    not  well  adapted  to    dry  farming     (Dry  Farming,  Widtsoe, 
Courtesy  Maomillan  Company.) 


DRY-LAND-  AGRICULTURE  241 

(b)  Evaporation. — The  amount  of  evaporation  is  one  of  the 
factors  that  determines  in  a  measure  the  value  of  a  region  for  dry 
farming,  since,  other  things  being  equal,  that  place  is  best  adapted 
to  this  practice  which  has  the  least  evaporation  (Fig.  104).  Xorth 
Dakota  with  a  rainfall  of  13  inches  has  31  inches  of  evaporation 
from  a  free-water  surface  during  the  six  summer  months,  while 
northern  Texas  with  a  like  rainfall  has  55  inches.  It  is  very 
evident  that  the  former  would  be  better  adapted  to  dry  farming. 

Rainfall  and  Evaporation  from  a  Free-Water  Surface  ' 


Places 

Annual 
precipitation 

Annual 
evaporation 

Lost  River,  Idaho 

iiic'ies 
8.47 

inches 

70 

Laramie   Wyoming 

9.81 

70 

Fort  Duchesne,  Utah    

6.49 

75 

St.  George,  Utah  

0.46 

90 

Tucson  Arizona        

11.74 

90 

Mohave  California                 .    .        

4.97 

95 

Fort  Yuinn   Arizona                           

2.84 

100 

(c)  Soils. — The  character  of  the  soil  is  of  much  importance, 
since  many  are  entirely  unfit  for  dry  farming,  because  of  some 
peculiarity  they  possess  which  renders  them  incapable  of  retaining 
the  moisture  necessary  for  crops.  In  selecting  land  for  dry  fann- 
ing, it  should  not  be  an  acid  soil  and  should  neither  be  too  open 
nor  too  impervious.  Coarse-grained  soils  (Fig.  105)  and  very  line- 
grained  ones  are  equally  objectionable  for  this  kind  of  agriculture. 
Layers  of  gravel  or  coarse  sand  or  hard  pan  are  serious  obstacles, 
since  in  the  one  case  the  water  passes  beyond  the  range  of  capillarity 
and  in  the  other  the  storage  reservoir  is  small  and  the  moisture 
cannot  percolate  deep  enough  to  be  retained  against  evaporation. 
Medium-grained  soils  (Fig.  10G)  with  uniform  texture  to  a  depth 
of  eight  or  ten  feet  furnish  best  conditions. 

Water  Requirements  of  Plants. — The  amount  of  water  used 
by  plants  in  arid  regions  is  about  one-half  more  than  in  humid 
regions.  In  T'tah  experiments  were  carried  on  for  six  years  on 
fertile  soils,  and  the  conclusion  is  that  an  average  of  ?">()  pounds  of 
water  per  pound  of  dry  matter  was  required. 

Briggs  and  Shantz  have  made  determinations  of  the  moisture  re- 
16 


242 


quiremeuts  of  a  large  number  of  plants.    The  results  of  their  inves- 
tigations are  given  in  the  following  table : 

Water  Required  to  Produce  One  Pound  of  Dry  Matter  at  Akron,  Col.* 


Millet 310 

Sorghum 322 

Corn 368 

Sunflower 683 

Wheat 513 

Teosinte 383 

Barley 534 

Oats 597 

Flax..  .  905 


Potato .- 636 

Cowpea 571 

Soybean 744 

Sugar  beet 397 

Red  clover 789 

Sweet  clover 770 

Alfalfa 831 

Tumble  weed 287 

Russian  thistle 336 


It  will  be  seen  that  the  amount  of  water  varies  from  287  to  905 
pounds  per  pound  of  dry  matter.  The  average  of  the  above  is  550 
pounds  of  water  for  each  pound  of  dry  matter.  Some  crops  are 
better  adapted  to  dry  land  agriculture  than  others  because  of  the 
fact  that  they  require  less  water,  while  some  have  habits  of  growth 
that  enable  them  to  resist  drouth.  Many  plants  must  bo  acclimated 
before  best  results  can  be  obtained. 

The  Utah  Station  found  that  cultivation  lessened  the  amount  of 
water  required. 

Pounds  of  Water  Required  to  Produce  a  Pound  of  Dry  Matter  of  Corn  s 


Not  cultivated 

Cultivated 

Sandy  loam       .      .  .            

603 

252 

Clay  loam  

535 

428 

Clay  

753 

582 

Type  not  given  

451 

265 

Loss  of  Water. — Kainfall  is  lost  from  the  soil  in  four  different 
ways,  namely :   run-off,  percolation,  evaporation,  and  transpiration. 

(a)  Run-off. — One  of  the  essentials  of  dry  farming  is  to  pre- 
vent loss  of  water  through  surface  run-off  by  putting  the  soil  in  con- 
dition to  absorb  the  rainfall.    It  is  impossible  to  prevent  some  loss 
because  of  the  torrential  rains  in  arid  regions.      The  soil  should 
be  kept  in  a  loose  condition,  so  as  to  absorb  water  as  rapidly  as 
possible. 

(b)  Percolation. — It  is  rarely  the  case  that  there  is  so  much 
rainfall  on  soils  well  adapted  to  dry  farming  that  water  gets  beyond 


DRY-LAND  AGRICULTURE 


243 


the  range  of  capillary  action.  Therefore  loss  by  percolation  is  in- 
significant. Percolation  into  the  upper  soil  layers  must  take  place 
very  rapidly  to  check  complete  saturation  of  the  surface  soil,  he- 
cause  this  would  result  in  more  or  less  run-off.  For  this  purpose 
the  looser  the  soil  the  hotter. 


Fia.    106. — A   deep,  medium-grained    soil    well    adapted    to   dry    funning.      Utah 
Farming,  Widtsoc.     Courtesy  MacmillaD  Company.) 


(Drv 


(c)  Evaporation. —  Arid  conditions  arc  very  well  adapted  to 
evaporation  of  water  from  the  soil  surface,  due  to  the  very  low  rela- 
tive humidity,  the  rarity  of  the  atmosphere  and  the  large  air  move- 
ment taking  place  in  arid  regions.  This  is  the  most  serious  source 
of  loss.  At  Salt  Lake  City  the  relative  humidity  in  summer  is  about 
35  per  cent,  while  in  humid  regions  the  average  is  from  ?">  to  80 


244  SOIL  PHYSICS  AND  MANAGEMENT 

per  cent.  As  a  general  rule,  the  surface  soils  are  dry  in  arid  regions, 
and  this  prevents,  in  a  measure  at  least,  a  large  loss  of  water,  since 
the  movement  oi'  water  through  dry  soil  is  very  slow.  Very  little 
evaporation  takes  place  within  the  interstices  of  the  soil  itself,  as 
has  been  shown  by  the  table  on  page  23'3.  Buckingham  has  shown 
that  the  amount  of  water  lost  by  transfer  upward  along  with  the 
air  in  the  process  of  aeration  amounts  to  no  more  than  one  inch 
in  six  years.  It  is  true,  however,  that  coarse  soils  lose  a  larger 
amount  in  this  way  than  fine-grained  ones,  but  the  loss  in  either 
case  may  be  neglected. 

(d)  Transpiration. — All  plants  take  water  through  the  root 
hairs  and  a  very  large  part  of  it  is  transpired  through  the  leaves. 
The  amount  of  water  used  in  this  way  constitutes  practically  all  that 
is  taken  up  by  the  plant  except  that  used  in  building  up  tissues, 
which  generally  amounts  to  only  a  small  fraction  of  the  total 
amount.  Transpiration  varies  with  certain  conditions,  both  of 
weather  and  soil,  and  in  general  the  factors  that  affect  evaporation 
from  the  soil  affect  transpiration  from  the  plant  (see  page  188). 
This  applies  to  plants  growing  in  humid  regions  as  well  as  under 
arid  conditions.  Transpiration  varies  inversely  as  the  relative 
humidity,  directly  with  temperature,  with  wind  velocity  and  direct 
sunshine ;  but  it  is  decreased  by  a  large  amount  of  plant  food  mate- 
rial dissolved  in  the  soil  moisture.  Arid  conditions  are  especially 
favorable  for  transpiration. 

It  must  be  remembered  also  that  weeds,  like  useful  plants, 
transpire  large  amounts  of  water  and  may  be  one  of  the  greatest 
sources  of  loss  unless  the  soil  is  kept  free  from  them.  Weeds  have 
no  place  on  any  farm,  but  more  especially  on  a  dry-land  farm. 
Eotmistrov  4  says,  "  Weeds  are  the  bitterest  enemy  of  field  culture 
and  the  best  friend  of  drought." 

METHOD  O-F  PREVENTING  LOSS  OF  WATER 

In  dry-farm  practice  every  means  must  be  used  for  preventing 
loss  of  moisture.  Other  crop  factors  sink  into  insignificance  in  com- 
parison with  this  one.  The  moisture  must  be  sufficient  not  only  to 
start  the  crop,  but  there  must  be  enough  stored  in  the  soil  to  mature 
it.  The  farmer  knows  that  every  pound  of  moisture  taken  from 
the  soil  that  does  not  go  through  the  crop  will  lessen  the  yield. 

The  loss  of  moisture  by  evaporation  is  prevented  to  some  extent 
by  the  crop  itself.  After  the  crop,  becomes  large  enough  to  shade 
the  ground  evaporation  is  greatly  retarded.  This  is  especially  true 


DRY-LAND  AGRICULTURE 


245 


of  non-tilled  crops.  The  air  enclosed  in  masses  of  vegetation,  such 
as  wheat,  oats,  millet,  clovers  and  similar  crops,  has  a  comparatively 
high  humidity,  so  that  evaporation  from  the  soil  is  retarded  and 
probably  almost  entirely  prevented  during  a  large  part  of  the  day. 
Jt  is  a  matter  of  common  observation  that  the  dew  remains  in 
heavy  oats  or  wheat  many  hours  after  sun-up  and  is  deposited  again 
several  hours  before  sunset.  This  will  effectively  prevent  much 
evaporation  from  the  soil.  While  the  humidity  of  the  air  in  these 
crops  of  semi-arid  regions  would  not  be  as  high  as  in  humid  ones, 
yet  the  difference  would  be  suflicient  to  lessen  the  evaporation. 

With  tilled  crops,  shading  aids  to  some  extent,  but  the  mulch 
is  the  important  factor.  When  the  crop  has  grown  to  such  she  that 
the  roots  are  well  distributed  through  the  soil,  moisture  has  very 
little  chance  of  reaching  the  surface,  because  of  the  network  of 
roots  which  are  absorbing  all  moisture  that  comes  within  reach. 

Tillage. — The  best  mean*  for  preventing  loss  of  water  is  by 
tillage,  by  which  a  mulch  is  maintained.  Various  experimenters 
have  found  that  cultivation  will  save  from  22  to  55  per  cent  of  the 
water  that  would  otherwise  evaporate. 

(a)  Depth  of  Tillage. — Tillage  produces  conditions  in  the  soil 
that  permit  very  slow  capillary  movement  by  forcing  soil  particles 
apart  so  that  the  films  of  water  cannot  pass  freely  from  one  to 
another.  As  a  general  rule,  the  deeper  the  mulch  the  more  effec- 
tive it  is  in  preventing  evaporation.  In  arid  regions  the  plowing 
is  one  of  the  most  fundamental  operations,  since  it  plays  two  very 
important  functions,  first,  in  producing  a  loose  mulch  for  retarding 
capillary  movement,  and,  second,  in  forming  a  deep  stratum  for 
absorbing  the  rainfall  and  retaining  it  afterward.  The  Utah  Sta- 
tion has  conducted  a  number  of  experiments  upon  depth  of  plowing 
and  the  results  show  that  eight  to  ten  inches  is  the  best  depth. 
When  increases  for  greater  depths  arc  obtained  they  are  usually 
too  low  to  cover  the  additional  expense. 

Yields  of  Wheat  for  Different  Depths  nf  Plnirinq.     Utah  Station. — Iin*hcls 

Per  A  i-rt-  5 


.)u  ah 
County 

Washing- 
ton County 

Tooole 

County 

Sovior 
County 

Plowing  S  inch  cv»  doop  
Plowing  10  inches  doop  

23.3 

28.4 

11.6 

12  0 

14.7 
14.<) 

5.3 

5.8 

Plowing  15  inches  doop  
Plowing  and  subsoil  ing  1S-20  indies 
deep  .  . 

10.9 
15.4 

15.2 
15.2 

14.8 
1fi.2 

as 

<>.4 

246  SOIL  PHYSICS  AND  MANAGEMENT 

Moderately  deep  plowing  is  very  essential,  since  it  prevents  loss 
by  surface  drainage. 

(b)  Fall  Plowing. — Summer  or  fall  plowing  is  especially  ad- 
vantageous because  it  permits  the  absorption  of  winter  rains  and 
snows,  and  if  cultivation  is  then  done  as  early  as  possible  in  the 
spring  a  large  amount  of  moisture  may  be  held  in  the  soil  for  the 
use  of  the  crop  in  the  fall  or  the  following  season.    If  the  plowing 
must  be  done  in  the  spring  it  should  be  done  as  early  as  possible  to 
catch  the  rains  and  hold  what  is  already  in  the  soil. 

The  disk  can  be  used  to  good  advantage  on  either  fall  or  spring 
plowing  to  produce  deep  mulches.  Even  on  stubble  the  disk  can 
be  used  to  advantage  as  soon  as  the  grain  is  removed.  If  a  crop  is 
seeded  in  the  fall,  one  of  the  very  necessary  things  is  to  produce 
a  mulch  as  early  in  the  spring  as  possible  with  some  implement 
adapted  to  that  purpose. 

(c)  Summer  Tillage  and  Cultivation. — Alternate  cropping 
provides  for  a  crop  every  other  year.     To  leave  the  land  idle  or 
occupied  with  weeds  would  be  of  no  benefit.     The  object  of  not 
cropping  during  one  season  is  to  store  moisture  for  the  crop  the 
following  year.    It  is  necessary  then  to  put  the  soil  in  condition  not 
only  to  absorb  the  rain  that  may  fall,  but  to  conserve  it  afterward. 
If  weeds  are  allowed  to  grow  the  moisture  will  be  lost.     To  avoid 
this  loss  summer  tillage  or  fallowing  is  practiced.     This  fits  the 
soil  for  absorbing  water,  for  conserving  it  from  evaporation  by  a: 
mulch  and  kills  weeds  that  use  it. 

Cultivation  of  crops  is  as  important  as  summer  tillage  and 
should  be  done  to  a  greater  depth  than  in  humid  regions.  It  may 
be  done  without  injury  to  the  roots  of  the  crops,  because  the  root 
systems  of  plants  develop  deeper  in  arid  than  in  humid  soils.  The 
mulch  produced  on  the  surface  should  not  be  too  fine,  but  made  up 
of  small  clods  mixed  with  fine  granular  material.  If  a  dust  mulch 
is  produced, -the  first  dash  of  rain  causes  the  soil  particles  to  run 
together  and  produces  a  somewhat  impervious  stratum  which  pre- 
vents rapid  absorption  and  water  is  lost  through  surface  run-off. 
Every  effort  must  be  made  to  maintain  a  mulch  until  a  network 
of  roots  is  developed  and  the  crop  is  large  enough  to  shade  the 
ground.  Another  objection  to  the  dust  mulch  is  that  the  fine  mate- 
rial is  so  easily  moved  by  the  wind  that  serious  loss  of  soil  may 
result. 

After  a  shower  falls,  the  mulch  should  be  renewed  as  soon  as 
possible.  Experiments  have  shown  that  of  the  water  lost  during 


DRY-LAND  AGRICULTURE  247 

the  first  week  after  a  rain  (>0  per  cent  occurred  during  the  first 
three  days,  hence  the  necessity  for  cultivation  as  soon  as  possible. 

(d)  Subsurface  Packing. — Newly  plowed  soil  contains  many 
large  air  spaces  and  is  too  open  for  retaining  water  against  evapora- 
tion. Subsurface  packing  is  resorted  to  for  closing  these  air  spaces 
and  preventing  excessive  loss  of  water  by  evaporation.  This  is 
accomplished  in  a  variety  of  ways.  Figure  107  shows  the  subsur- 
face packer  which  is  used  for  this  purpose.  The  wedge-like  wheels, 
five  inches  apart,  crowd  the  soil  to  both  sides,  thus  compacting  the 
subsurface,  but  leaving  a  mulch  on  the  surface.  This  implement 
was  invented  by  Mr.  H.  YV.  Campbell,  of  Lincoln,  Nebraska,  one 
of  the  pioneers  in  dry  farming. 

Other  methods  are  resorted  to  for  compacting  the  subsurface, 


FlO.    107. — Cuinpbi-11  Subsurface  Packer. 

such  as  using  the  disk  set  straight.  The  ordinary  smooth  roller 
would  not  be  desirable  for  this  purpose,  because  the  compact  ion 
that  it  produces  renews  capillarity  at  the  surface  and  would  cause 
a  loss  of  moisture  unless  a  mulch  were  again  produced  on  the  sur- 
face. In  fact,  the  smooth  roller  should  never  be  used  on  a  dry  farm, 
as  the  flat  surface  produced  encourages  the  soil  to  blow.  The  cor- 
rugated roller  leaves  the  soil  rough  and  this  prevents  or  at  least 
greatly  lessens  blowing.  The  rolling  should  not  be  done  parallel 
to  the  direction  of  the  prevailing  winds,  but  at  right  angles  to  it. 

(e)  Storing  of  Rainfall. — A  very  important  factor  in  dry  farm- 
ing is  the  storing  of  the  rainfall  of  one  year  in  the  soil  for  the 
use  of  the  crop  the  coming  season.  The  major  part  of  the  /.one 
in  which  the  water  is  stored  should  be  sufficiently  deep  so  that  it  is 
beyond  the  depth  of  ready  capillary  movement  to  the  surface  and 


248 


SOIL  PHYSICS  AND  MANAGEMENT 


within  the  limit  of  the  root  zone  for  plants  under  arid  conditions. 
This  varies  from  eight  to  ten  feet  or  more  in  depth.  Experiments 
in  Utah  showed  as  much  as  95^  per  cent  of  the  water  which  fell 
as  rain  and  snow  during  the  winter  was  found  stored  in  the  first 
eight  feet  of  soil  in  the  spring.  Atkinson  found  that  at  the  Mon- 
tana Station  soil  which  contained  7.7  per  cent  of  moisture  in  the 
fall  contained  11.5  per  cent  in  the  spring  and  after  proper  summer 
tillage  contained  11  per  cent  in  the  fall.  The  following  tahle  shows 
the  amount  of  water  that  may  he  stored  in  the  soil  during  the 
winter : 

Percentage  of  Water  in  Each  Foot  of  Soil  to  a  Depth  of  Eight  Feel 8 


First 
foot 

Second 
foot 

Third 
foot 

Fourth 
foot 

Fifth 
foot 

Sixth 
foot 

Seventh 
foot 

Eighth 
foot 

Aver- 
age 

Sept.  8,  1902 
April  24,  1903 
Increase  

6.37 
19.29 
12.92 

7.32 
19.08 
11.76 

8.17 
18.83 
10.66 

8.55 
16.99 
8.44 

8.26 
13.61 
5.35 

9.29 
12.62 
3.33 

10.10 
12.24 
2.14 

10.38 
12.37 
1.99 

8.56 
15.63 
7.07 

Aug.  24,  1906 
May  1,  1907 
Increase 

8.33 
18.17 
9.84 

7.63 
16.73 
9.10 

8.42 
17.96 
9.54 

9.66 
16.88 

7.22 

11.30 
16.59 
5.29 

10.75 
16.25 
5.50 

9.59 
14.98 
5.39 

7.93 
13.48 
5.55 

9.20 
16.38 
7.18 

It  will  he  noted  that  the  increase  of  moisture  amounted  to  eight 
inches  for  the  eight  feet  of  soil.  Water  storage  in  a  soil  is  impos- 
sible when  a  crop  of  weeds  is  growing. 

System  of  Cropping. — There  can  be  no  continuous  cropping 
in  dry-land  agriculture  as  in  humid  regions,  because  the  rain- 
fall is  not  usually  sufficient  to  grow  two  crops  in  succession. 
However,  if  the  rainfall  of  two  seasons  can  be  used  for  growing  a 
single  crop,  profitable  results  may  be  obtained.  The  conservation 
of  this  moisture  from  one  season  to  the  next  is  the  most  important 
problem  in  this  kind  of  agriculture.  The  possibilities  of  raising 
grain  under  dry  farming  methods  are  seen  in  figures  108,  109 
and  110. 

Continuous  Cropping  vs.  After  Fallow.     Average  Remits  for  All  Years  Tested, 
Montana  Station"1    ([iushcls  Per  Acre) 


Kubanka 
spring  wheat 

White  hullesj 
barley 

Jixtj 

OF 

Con- 
tinuous 

'-day 

kt.x 

Sub-station 

Con- 
tinuouH 

Aft«r 
fallow 

Con- 
tinuous 

After 
fallow 

After 
fallow 

Dawson  County 

15.18 
16.98 
7.73 
14.18 

17.57 
20.80 
19.32 
17.35 

l.Y'17 
15.02 
14.90 
13.29 

•JO.'.  10 

28.31 
20.33 
11.95 

31.17 
30.31 
13.75 
28.90 

51.00 
40.03 
47.94 
34.56 

Rosebud  County 

Yellowstone  County  .... 

Chouteau  County  .  . 

Fio.   10S. — Turkey  Red  Fall  Wheat,  without  irrigation,  yield  5S  bushels   per  nrre.     (Mon- 
tana Station,  Bui.  74/) 

Fio.    100. — White  Hulle.4.1  Barley  on  land  continuously  cropped. 

Fio.    110. — White    Ilulless    Barley  on  land  fallowed  the  previous  year.     (Bui.  74,  Montana 

Station.) 


250 


SOIL  PHYSICS  AND  MANAGEMENT 


The  results  show  that  fallowing  gives  considerable  increase  over 
continuous  cropping.  The  longer  this  is  continued  the  greater  the 
difference.  Whether  alternating  crops  with  summer  tillage  is 
profitable  will  be  determined  largely  by  local  soil  and  climatic  con- 
ditions that  influence  the  cost  of  production. 

Summer  Tillage  With  Alternate  Cropping  vs.   Continuous  Cropping*  Noith 
Dakota  Station  (Bushels  Per  Acre) 


Station 

Treatment 

Wheat 

Oats 

Barley 

Corn* 

Edgelev.  . 

Continuous  

13.2 
14.8 
15.6 
27.8 
14.2 
19.8 
11.2 
21.5 

26.8 
42.5 
30.8 
51.1 
29.5 
46.0 
34.8 
48.6 

17.0 
20.0 
25.5 
32.5 
16.1 
28.8 
23.7 
31.8 

3610 
3400 
3750 
2880 
6890 
7370 
5840 
5540 

Summer  tillage  .... 
Continuous  

Dickinson  

Summer  tillage  .... 
Continuous  

Willi«?t/in 

Hettinger  

Summer  tillage  .... 
Continuous  

Summer  tillage  

Average  increase  for  S 

ummer  tillage  

7.5 

16.6 

7.7 

-225 

*Pounds. 

It  will  be  seen  from  this  table  that  summer  tillage  gave  an 
increase  for  wheat,  oats  and  barley,  but  best  results  were  obtained 
for  corn  by  continuous  cropping. 

Crops  for  Dry  Farming. — In  no  kind  of  agriculture  is  the 
adaptation  of  the  crop  to  the  environment  of  greater  consequence 
than  in  dry  farming.  In  general,  the  crops  should  be  sut'h  that 
a  maximum  growth  is  secured  with  minimum  water  requirements, 
and  the  crops  that  meet  this  condition  will  be  best  adapted  to 
dry-land  agriculture.  Alfalfa  is  an  exception,  but  its  deep-root- 
ing character  has  fitted  it  for  securing  a  large  amount  of  water. 
Most  crops  have  the  power  of  adapting  themselves  to  some  extent  to 
the  conditions  of  climate  after  a  few  years,  but  the  dry-land  farmer 
needs  a  variety  of  crops  that  have  been  tried  and  developed  by 
selection  so  that  they  resist  the  unusual  conditions  to  which  they 
are  subjected.  Upon  the  selection  of  the  crop  and  seed  may  depend 
the  success  or  failure  of  his  efforts. 

(a)  Wheat  is  the  principal  crop  for  the  dry-land  farmer.  All 
over  the  arid  and  semi-arid  regions  wheat  has  proved  to  be  one  of 
the  best  drouth -resistant  crops  that  can  be  grown.  In  the  dry-land 
regions  of  other  continents  wheat  has  been  grown  for  many  cen- 
turies, and  certain  varieties  have  been  developed  which  are  welt 


DRY-LAND  AGRICULTURE  251 

adapted  to  arid  conditions.  Both  spring  and  winter  wheats  are 
grown,  the  latter  being  much  more  desirable  where  the  climate  is 
suitable.  Spring  wheats  are  grown  largely  from  Nebraska  north 
through  the  Dakotas  because  of  the  severe  winters.  Two  varieties 
of  spring  wheat  are  grown,  the  common  spring  wheat  and  the 
Durum  or  Macaroni.  The  latter  was  introduced  from  Russia  and 
has  proved  to  be  an  excellent  variety.  The  semi-hard  winter  wheats 
are  grown  over  extensive  areas,  the  most  hardy  varieties  being 
Turkey  Red,  Kharkof  and  Crimean,  all  originating  in  semi-arid 
Russia. 

The  yield  of  wheat  on  the  dry  farm  is  of  a  great  deal  of  conse- 
quence because  it  is  the  chief  money  crop.  Winter  wheat  yields 
better  than  spring  wheat.  It  usually  pays  to  grow  either  on  summer 
tilled  land.  In  the  dry-farm  experiments  in  Montana  the  average 
yield  of  Turkey  Red  was  37.7  bushels  per  acre,  while  the  spring 
wheat,  Kubanka,  was  18.4  bushels,  or  ahout  half  as  much.  In 
Utah  Turkey  Red  produced  28.1  bushels,  while  the  best  spring 
wheat  for  the  same  years  produced  14.6  bushels  per  acre. 

(b)  Oats  are  beginning  to  be  recognized  as  a  good  dry-land 
crop,  either  for  hay  or  grain.    Of  the  spring  varieties  the  Sixty  Day 
has  proved  to  be  best,  principally  because  it  ripens  two  weeks  earlier 
than  other  varieties.     A  winter  variety,  the  Boswell,  that  has  been 
tried  in  Utah,  promises  well.     Tn  1907  and  1908  Sixty  Day  oats 
yielded  42.3  bushels  per  acre,  while  the  Boswell  gave  40.1  bushels. 
At  the  Montana  Station  the  yield  of  Sixty  Day  was  37. (i  bushels. 

(c)  Rye  is  one  of  the  best  dry-land  grains.     It  resists  drouth 
better  than   almost  any  other  cereal.      The  fall   rye   at   Montana 
yielded  28.5  bushels  per  acre.     The  most  serious  objection  to  it  is 
its  persistence  in  the  field  after  once  seeded.     It  may  be  used  to 
good  advantage  as  a  green  manure. 

(d)  Barley  is  one  of  the  cereals  well  adapted  to  dry-land  if 
seeded  very  early  in  the  spring  so  that  it  gets  a  good  start  before  the 
dry,  hot  weather  begins.    The  hulless  varieties  seem  to  do  best.    Tn 
Montana  as  an  average  of  all  tests  on  different  fields  the  yield  of 
the  White  Hulless  was  17.8  bushels  per  acre,  while  the  California 
yielded  one  bushel   more.     Tn   Xorth   Dakota   an  average  of  23.8 
bushels  was  obtained.     One  winter  variety  has  been  grown. 

(e)  Corn  has  not  been   grown    very   extensively   on    dry -land 
farms  because   it   is   not    well    adapted   to   the   temperature   condi- 
tions  found   in   arid    regions.       Corn    does  best   where   the   nights 
are  warm,  and  in  arid  regions  the  radiation  is  so  great  as  to  lower 


252 


SOIL  PHYSICS  AND  MANAGEMENT 


the  temperature  very  much  during  the  night.  Corn  has  com- 
paratively low  water  requirement  and  produces  more  dry  matter 
for  the  water  used  than  almost  any  other  crop.  Several  strains 
have  heen  developed  that  resist  drouth  well.  When  acclimated 
seed  is  used,  seed  bed  properly  prepared  and  the  crop  well  culti- 
vated, a  failure  rarely  ever  occurs.  In  almost  every  season  suf- 
ficient fodder  is  produced  to  pay  for  the  crop,  and  in  the  more 
favorable  years  good  yields  of  grain  are  obtained.  Its  principal 
value  lies  in  the  forage  it  produces.  Figure  111  shows  corn  grown 


Fid.   111. — Corn  grown  on  dry -land  farm.     Note  low  stalks.     Utah. 

on  a  dry-land  farm.     The  stalks  are  not  so  coarse  as  in  humid 
areas  and  make  better  feed. 

(f)  Spelt  and  Emmer  have  been  recommended  as  crops  well 
adapted  to  semi-arid  conditions.    They  were  imported  from  Russia, 
where  they  have  been  grown  quite  extensively  as  feed  for  stock. 
They  are  very  closely  related  to  wheat,  but  the  hull  remains  attached 
as  with  barley. 

(g)  Sorghum  is  one  of  the  principal  drouth-resistant  crops  and 
yields  as  much  as  seven  tons  per  acre.    Its  chief  use  is  for  forage. 

(h)  Kafir  and  Milo  Maize. — These  are  well  adapted  to  the 
Great  Plains  south  of  Nebraska  and  parts  of  California.  The 
temperature  of  the  higher  altitudes  is  too  low  for  its  growth.  These 


DRY-LAND  AGRICULTURE 


253 


are  used  both  for  forage  and  grain.  In  the  southern  part  of  the 
Great  Plains  in  Kansas,  Oklahoma,  Texas  and  New  Mexico  these 
form  a  very  important  crop.  Jardine  °  states  that  the  average  yield 
of  shelled  grain  from  milo  maize  was  -10  bushels  per  acre  in  the 
Panhandle  of  Texas. 

Where  a  severe  drouth  occurs  these  crops  stop  growing  but  re- 
main alive.  They  start  quickly  again  when  rains  come. 

(i)  Alfalfa. — No  crop  has  been  of  greater  value  on  the  irri- 
gated land  of  the  West  than  alfalfa,  and  it  is  proving  to  be  a  very 
valuable  crop  on  the  dry-land  farm  as  well.  It  is,  however,  very 
difficult  to  start  under  arid  conditions.  The  fact  that  the  roots 
penetrate  to  such  a  great  depth  in  these  dry-land  areas  makes  it 


FIG.   112. — Dry-farm  potatoes.      Utah. 

adapted  to  using  the  moisture  stored  to  a  great  depth  in  the  sub- 
soil, and  no  single  season's  drouth  will  affect  it  seriously  after  it 
becomes  thoroughly  established  in  the  soil.  Thick  seeding  must 
be  avoided.  It  is  better  adapted  to  light  and  medium  soils  than 
to  heavy  clays.  Cultivation  is  as  essential  in  growing  alfalfa  as  for 
any  other  crop.  The  seed  crop  is  one  of  the  most  profitable  of  the 
alfalfa  field.  For  producing  seed  it  is  best  to  plant  the  alfalfa  in 
hills  or  rows  so  that  it  may  be  cultivated.  Tt  may  be  necessary 
to  thin  it  to  one  plant  every  six  to  twelve  inches.  The  second  crop 
is  usually  left  for  seed,  the  amount  of  seed  produced  varying  from 
150  to  300  pounds  per  acre. 

(j)  Potatoes  (Fig.  11  '2}  are  coming  to  he  looked  upon  as  one 
of  the  staple  crops  of  dry-land  agriculture.  With  a  rainfall  of  1? 
inches  or  more  potatoes  produce  excellent  crops,  both  in  yield  and 


254 


SOIL  PHYSICS  AND  MANAGEMENT 


quality.     An  average  yield  of  123  bushels  per  acre  was  produced 
on  the  Montana  Experiment  stations  in  the  dry-farming  areas. 

Seeding. — In  semi-arid  regions  seeding  must  be  done  more 
carefully  than  in  humid  regions.  A  deep  mellow  seed  bed  must 
be  thoroughly  prepared  and  too  much  work  cannot  be  expended 
upon  it.  The  seed  bed  should  be  such  as  to  act  as  a  storage  reser- 
voir for  water  and  sufficiently  compact  so  that  the  moisture  will  be 
near  the  surface  to  germinate  the  seed.  After  the  seed  is  planted 
or  during  the  process  of  planting  the  soil  should  be  compacted 
around  the  seed.  For  this  reason  the  press  drill  should  be  used 
quite  generally  in  seeding.  It  permits  uniform  distribution  and 
covering  of  seed.  Broadcast  seeding  invites  failure. 

Yieds  of  Loftfunise  Wheat  With  Different  Methods  of  Seeding,10  Utah  Station 
(Bushels  Per  Acre) 


County 

Method  of  seeding 

1904 

1905 

1906 

1907 

190S 

k  Average 

[Broadcast  

12.5 

5.5 

15.0 

16.0 

15.3 

12.9 

Tooele.  . 

\  Drilled 

15.2 

13.5 

16.4 

27.5 

24.9 

19.9 

[Cross  drilled  .  . 
[Broadcast  . 

13.5 
16.7 

13.0 
13.9 

13.3 
25.6 

19.9 
8.6 

19.2 
12.9 

15.9 
15.6 

Juab  .... 

j  Drilled  

24.5 

16.9 

33.5 

37.6 

33.4 

29.2 

(Cross  drilled  .  . 

18.0 

8.5 

24.4 

30.0 

11.9 

18.6 

From  the  preceding  table  it  will  be  seen  that  the  drilled  wheat 
gave  an  increase  of  7.0  bushels  in  one  case  and  13.6  bushels  in 
another  over  the  broadcasted. 

On  semi-arid  land  it  might  be  supposed  that  deep  seeding  would 
be  necessary.  The  depth  must  depend  upon  the  character  of  the 
soil  and  the  amount  of  moisture  it  contains.  In  heavy  clay  plant- 
ing should  be  from  one  to  one  and  one-half  inches,  while  planting 
in  sandy  loams  may  be  as  deep  as  three  inches.  Where  wheat  was 
planted  three  inches  deep  in  heavy  clay  the  yield  for  an  average 
of  five  years  was  18.3  bushels,  while  where  the  planting  was  done 
at  one  and  one-half  inches  the  yield  was  26.9  bushels  per  acre.11 

The  amount  of  seed  to  the  acre  should  be  a  little  more  than  half 
that  required  in  humid  regions.  A  heavy  seeding  results  in  almost 
certain  failure.  It  very  frequently  happens  that  the  moisture  in 
the  soil  will  be  sufficient  to  start  the  plants  of  a  light  seeding  in 
fine  shape,  while  those  of  a  heavy  seeding  would  all  be  stunted. 


DRY-LAND  AGRICULTURE 


255 


The  Colorado  Station  recommends  the  following  amounts,  al- 
though this  may  vary  with  the  condition  of  the  soil: 

Pounds  of  Seed  Per  Acre  for  Different  Crops  lt 


Crop 

Pounds 
per  acre 

Crop 

Pounds 
per  acre 

Wheat 

30  to  40 

Milo  maize  for  grain 

5  to    8 

Barley  .  .       '  . 

35  to  50 

Dwarf  Essex  rape.    . 

3  to    5 

Flax 

20 

Brome  grass 

20 

Spelt  and  emmer  

45 

Alfalfa  for  hay  

12  to  20 

Millet 

10 

Alfalfa  cultivated  for  seed 

2  to    3 

Sorghum  for  forage 

25 

Sweet  clover 

20  to  25 

Kafir  corn  for  forage.  .  .  . 

25  to  30 

Corn,  single  grains,  15  to  18  inches  apart. 

Merrill  of  Utah  recommends  that  oats  and  barley  be  seeded  at 
the  rate  of  three  pecks  per  acre;  rye,  two  pecks;  alfalfa,  six  pounds, 
and  other  crops  in  proportion. 

Acclimated  Seed. — The  seed  to  be  planted  on  a  dry-land 
farm  should  have  been  grown  under  semi-arid  conditions. 
Farmers  from  humid  regions  frequently  take  seed  with  them  when 
they  go  on  the  dry  farm  and  crop  failure  results.  Usually  several 
years  are  required  for  a  crop  from  humid  regions  to  become 
thoroughly  adapted  to  its  new  conditions  so  that  it  will  produce  well. 
1 1  is  far  better  for  the  farmer  to  obtain  seed  already  accustomed 
to  dry  conditions. 

QUESTIONS 

1.  Upon  what  three  things  does  the  adaptation  of  land  for  dry  fanning 

depend  ? 

2.  What  conditions  of  soil  are  best?     What  are  objectionable? 

3.  From  the  standpoint  of  water  requirements,  what  are  some  of  the  {jowl 

crops  for  dry  farming? 

4.  Tlow  does  cultivation  lessen  the  water  requirement  of  crops? 

5.  Why  do  crops  on  summer  fallow  produce  more  than  where  cropped  con- 

tinuously? 
0.  What  conditions  in  arid  regions  make  a   large  run-olF  possible? 

7.  What  conditions  allow  a  large  evaporation? 

8.  What   is  the  most  desirable  depth   to  plow  in  dry  farming? 

9.  Why   is  fall   plowing  more  desirable  under   dry-farm   conditions? 

10.  dive  the   advantages   in    the   use  of   the   subsurface   packer. 

11.  To  what  extent  may   the  fall   and  winter  rain  and  snowfall  be  stored 

in  the  soil   for  crops? 

12.  What  alxHit  weeds  on  a  dry-hind  farm? 
IH.  How  does  transpiration  vary? 

14.  What  important  points  should  be  observed  in  selecting  crops  and   seed 
for  the  drv  farm  ? 


256  SOIL  PHYSICS  AND  MANAGEMENT 

15.  Give  the  advantages  of  wheat  for  the  dry-land  farm. 

16.  Why  is  a  fall  or  winter  variety  more  desirable  than  a  spring-sown  one? 

17.  What  special  advantages  has  corn  for  semi-arid  regions? 

18.  Why  is  alfalfa  a  good  dry-hind  crop?     How  is  a  seed  crop  produced? 

19.  What    precautions    must   be   taken    in    seeding    the    crop    in    dry-land 

farming? 

20.  What  is  meant  by  acclimated  seed?     Why  is  it  important? 

REFERENCES 

1  Widtsoe,  J.  A.,  Dry  Farming,  1911,  p.  132. 

*  Brigga,  L.  J.,  and  Shantz,  H.  L.,  Journal  of  Agricultural  Research,  vol. 

Ill,  No.  1,  1911,  pp.  58-<50. 

I  Wiltsoe,  J.  A.,  Dry  Farming,  1911,  p.  185.     Principles  of  Irrigation  Prac- 

tice, 1914,  p.   141. 

4  Rotmistrov,  V.  G.,  Nature  of  Drought,  English  edition,  1913. 
"Merrill,  L.  A.,  A  Report  of  Seven  Years'  Investigation  of   Drv   Farming 

Methods,   1910,  p.   133. 

•Widteoe,  J.  A.,  Dry  Farming,  1911,  p.  114. 

T  Atkinson,  A.,  and  Nelson,  J.  B.,  Bulletin  74,  Montana  Station,  1908,  p.  83. 
"Thysell,   J.   C.,   and   others,   Bulletin    110,    North    Dakota    Station,    1915, 

pp. 183-185. 

•  Jardine,  W.  M.,  Circular  12,  Bureau  of  Plant  Industry,  V.  S.  D.  A.,  Dry- 

Land  Grains,  1908,  p.  6. 

"Merrill,  L.  A.,  Bulletin  112.  Utah  Station,  A  Report  of  Seven  Years'  Inves- 
tigation of  Dry  Farming  Methods,  1910,  p.  139. 

II  Op.  Cit.,  p.  138. 

"Cottrell,   H.   M.,   Bulletin    145,   Colorado   Station,   Dry-Land    Farming   in 
Eastern  Colorado,  1910,  p.  23. 

General  References.— Olin,  W.  H.,  Bulletin  103,  Colorado  Station, 
The  Thorough  Tillage  System  for  the  Plains  of  Colorado,  1905.  Failyer, 
G.  H.,  Farmers'  Bulletin  266,  U.  S.  D.  A.,  1906.  Jardine,  W.  M.,  Bulletin 
100,  Utah  Station,  Arid  Fanning  Investigations,  1906.  Scofield.  C.  S., 
Bulletin  103,  Bureau  of  Plant  Industry,  Dry  Farming  in  the  Great  Basin. 
1907.  Campbell,  H.  W.,  Soil  Culture  Manual,  1907,  Lincoln.  Neb.  Nelson, 
Elias,  Bulletin  62,  Idaho  Station,  Dry  Farming  in  Idaho,  1908.  Burr, 
W.  W.,  Bulletin  114,  Nebraska  Station, 'Storing  Moisture  in  the  Soil,  1910. 


CHAPTER    XXI 

CONTROL  OF  MOISTURE 
IV.  IRRIGATION 

IRRIGATION  may  be  practiced  in  any  region  where  the  normal 
rainfall  is  not  sufficient  to  grow  maximum  crops  or  where  the 
rainfall  is  deficient  during  any  part  of  the  season.  The  profit 
realized  will  depend  upon  the  crop  grown,  the  increase  in  yield  over 
no  irrigation,  the  cost  of  applying  water,  and  the  price  of  the  crop. 
The  practice  is  usually  confined  to  arid  regions  because  irrigation  is 
absolutely  necessary  under  those  conditions  to  produce  any  crop 
whatever,  or  to  semi-arid  regions  where  irrigation  will  give  larger 
yields  and  in  some  very  dry  years  would  insure  a  crop  where  other- 
wise there  would  be  none.  Irrigation  is  practiced  to  a  very  limited 
extent  in  humid  climates,  even  in  Florida  with  from  fifty  to  sixty 
inches  of  rainfall  and  in  other  states  with  thirty  to  forty  inches. 
In  these  regions  water  is  applied  in  a  very  intensive  form  of  agri- 
culture or  to  special  crops  which  command  a  high  price,  thus  jus- 
tifying the  expense.  In  some  European  countries  sewage  is  some- 
times applied  to  soils,  thus  furnishing  both  water  and  plant  food. 
In  China  and  Japan  irrigation  is  an  almost  universal  practice,  even 
where  much  of  the  land  receives  a  fair  natural  supply  of  water  in  a 
well  distributed  rainfall. 


Some  Irrigation  Projects  in  Western  United  States 


Salt  River,  Arizona 

Yuma,  Arizona-California 

Uncompahgre,  Colorado 

Boise,    Idaho 

Minidoka,  Idaho 

Flathead,  Montana  

Milk  River,  Montana 

Sun  River,  Montana 

North  Platte,  Nebraska-Wyoming. 
Shoshone,  Wyoming.  . 


Approximate 


$10,000,000 
7,(XX),000 

"1,000.  (XX) 

S,7(X),0<)0 
4,400.000 
1.2."  0,000 

i.ono.ooo 

1.  (XX).  000 
ir>.200.000 

:t.xw.(xx) 


Aero*  to  ho 
irrigated 


219.000 


140.000 
243,000 
11S.OOO 
1.72,000 
210,000 

2i(i.noo 

1  29,000 
HVi.OOO 


17 


258 


SOIL  PHYSICS  AND  MANAGEMENT 


The  area  of  land  that  may  ultimately  be  brought  under  irriga- 
tion is  small  in  comparison  with  the  total  dry-land  area,  because 
the  total  supply  of  water  is  not  sufficient  for  more  than  one-tenth 
of  the  dry  land.  At  present  only  about  one  per  cent  of  the  land  in 
the  western  states  is  irrigated.  The  building  of  such  reservoirs 
as  are  given  in  the  preceding  table  is  extending  the  irrigated  area 
more  than  was  supposed  to  be  possible  a  few  years  ago. 

Area  and  Projects. — In  1009,  13,739,499  acres  of  land  were 
irrigated  in  the  arid  states.  This  was  an  increase  of  82  per  cent  in 
ten  years.  In  1910  the  projects,  then  started,  will  be  capable  of 
irrigating  19,335,711  acres  when  fully  under  way.  The  total  area 
included  in  the  projects  is  31,112,110  acres.  In  addition  to  the 


FIG.  113.  Fia.  114. 

Fio.   113. — Conduit  for  conducting  water  to  where  it  maybe  used  for   irrigation.      (U.  S. 

Reclamation   IService.) 

Fia.   114. — Concrete-lined  canal  that  permits  no  loss  by  seepage.        (U.  S.   Reclamation 

Service.) 

above,  724,800  acres  of  land  were  irrigated  in  humid  areas,  nearly 
all  of  which  was  for  the  growing  of  rice. 

The  United  States  Reclamation  Service,  established  in  1902, 
was  to  use  the  money  from  the  sale  of  public  lands  in  the  arid  states 
in  the  construction  of  irrigation  systems.  Under  the  direction  of 
Dr.  F.  H.  Newell  immense  projects  have  been  started,  many  of 
which  have  been  completed,  and  by  which  large  areas  have  been 
reclaimed  and  added  to' the  country  as  some  of  its  most  valuable 
assets. 

Sources  of  Water. —  (a) Diversion  of  Streams. — The  com- 
mon source  of  water  for  irrigation  has  been  the  diversion  of  parts 
of  streams  at  a  height  above  where  it  is  to  be  used  and  conducting 
it  by  means  of  canals,  tunnels,  conduits  and  ditches  to  where 
it  is  to  be  distributed  over  the  land  (Figs.  113  and  114). 


IRRIGATION  259 

Water  is  sometimes  conducted  for  many  miles,  passing  through 
hills  aud  over  valleys  and  gorges,  lii  the  case  of  the  (Junuison 
tunnel  of  Colorado,  the  Gunnisoii  river  is  diverted  from  its  course 
and  carried  through  a  tunnel  almost  six  miles  long,  pouring  into 
the  Uucompahgre  Valley,  where  it  is  used  to  irrigate  140,000  acres. 

(b)  Reservoirs. — In  many  places  in  the  arid  regions  of  this 
and  other  countries  dams  have  been  built  across  gorges  or  narrow 
valleys,  producing  lakes  or  reservoirs  whose  water  is  used  in  the 
irrigation  of  tillable  land  farther  down  the  valley.     In  this  way 
the  rains  and  snows  of  winter,  which  would  otherwise  be  lost,  are 
held  for  the  use  of  crops  at  a  time  when  the  water  of  the  stream 
is  entirely  insufficient  for  the  purpose.     The  Roosevelt  dam  across 
the  Salt  Jiiver  in  Ari/omi  is  a  good  illustration  (Fig.  115).     Here 
sufficient  water  is  stored  for  irrigating  2 11), 000  acres.     This  dam, 
curved  upstream,  is  284  feet  high  and  1)10  feet  long,  with  a  thick- 
ness at  its  base  of  108  feet  and  20  feet  at  the  top.     It  forms  a  lake 
or  reservoir  25  miles  long  and  from  one  to  two  miles  wide  and  con- 
tains 1,367,000  acre-feet  of  water.    Many  similar  systems  have  heen 
constructed  by  the  government,  or  arc  under  way,  that  will  irrigate 
from  10,000  to  225,000  acres  each,  making  a  total  of  over  3,000,000 
acres  irrigated  by  these  projects  (  Fig.  1  Hi). 

(c)  Pumping  from  Some   Subterranean  Supply. — In   some 
localities  in  arid  regions  extensive  underground  reservoirs  of  water 
occur  sufficiently  near  the  surface  to  be  pumped  for  irrigation  pur- 
poses.    In  other  regions  artesian   wells  may   furnish   a   bountiful 
supply.    Where  irrigation  is  practiced  in  humid  regions  pumping  is 
the  usual  method.     The  rice  fields  of  Arkansas  and  Louisiana  are 
irrigated  in  this  way. 

(d)  Pumping  from   Streams   or  Canals.— In   Egypt,  India, 
China  and  Japan  much  of  the  water  for  irrigation  is  pumped  on  the 
land  by  means  of  hand  or  foot  power.     Sometimes  cattle  or  donkeys 
are  used  for  this  purpose. 

Preparation  of  the  Land  for  Irrigation. — The  first  step  in 
preparing  the  land  for  irrigation  is  the  removal  of  the  vegetation 
(Fig.  117).  The  character  of  this  varies  with  the  amount  of  rain- 
fall from  stunted  grass,  sage  brush,  greasewood.  and  mosquite  to 
the  remains  of  heavy  forest*.  The  cost  of  clearing  varies  from  two  to 
five  dollars  per  acre  for  most  lands  to  as  much  as  one  hundred  and 
fifty  dollars  per  acre  for  forests.  After  the  vegetation  if?  removed 
the  land  must  be  graded  so  that  the  water  may  be  uniformly  ap- 
plied. Many  tracts  are  so  flat  that  very  little  grading  is  necessary. 


260 


SOIL  PHYSICS  AND  MANAGEMENT 


FIG.  115. 


•      . 


FIG.  116. 

Fio.  115. — Roosevelt  Dam,  Salt  River,  Arizona.     (U.  S.  Reclamation  Service.) 
Fio.   116. — Granite  Reef  Diversion  Dam;  Salt  River  Project,  Arizona.     (U.  8.  Reclamation 

Service.) 


IRRIGATION 


261 


Usually  there  are  depressions  to  he  filled  or  slight  elevations  to 
he  removed.     The  ohject  is  not  to  level  the  land,  but  to  reduce 


.  117. 


Fio.  118. 
Fin.   117. — Desert  lands  and  Homestead,  Iluntloy  Trojort,  Montana.      (U.  S.  Rrrlnmntion 

Service.) 

Fio.    118.— Wheat    firl.l,    Minidoka    Projcrt.     Malio.      Yield   00  bushels   per   acre.       (U.    S. 

Kerlamation   Service  ) 

it  to  a  uniform  slopo  so  that  water  will  spread  over  i(   uniformlv 
(I-V  IIS). 

Character  of  Water  Used  for  Irrigation.      In  humid  regions 


262 


SOIL  PHYSICS  AND  MANAGEMENT 


the  water  of  streams  carries  but  little  soluble  material,  but  in  arid 
and  semi-arid  regions,  where  the  great  necessity  for  irrigation 
exists,  both  soil  and  water  may  contain  alkali  in  considerable  abun- 
dance. While  the  excess  of  alkali  in  irrigated  lands  is  due  usually 
to  the  salts  in  the  soil,  yet  it  is  in  many  cases  due  in  part,  and  some- 
times wholly,  to  the  salinity  of  the  water  which  is  being  used  for 
irrigation.  The  salts  thus  carried  accumulate  in  the  soil,  pro- 
ducing very  injurious  results.  Forty  grains  of  salts  per  gallon  is 
usually  assigned  as  the  limit  for  irrigation  waters.  This,  however, 
depends  upon  the  character  of  the  substances  in  solution.  In  Cali- 
fornia the  limit  lies  in  all  cases  below  70  grains.  The  clanger  of 
using  irrigation  water  containing  considerable  salts  depends  very 
largely  upon  the  drainage  of  the  land  irrigated  or  the  methods  of 
preventing  their  accumulation. 

Suspended  Matter  in  River  Waters  l 


River 

Parts  per  million 

Minimum 

Maximum 

Belle  Fourchc,  at  Belle  Fourche,  South  Dakota  

56 
18 
741 
0 
32 
0 
44 
8 
40 
62 

7,120 
2,860 
30,800 
16,800 
4,090 
1,480 
11,400 
83,900 
6,940 
3,450 

Bighorn,  at  Fort  Custer,  Montana 

Colorado,  at  Yuma,  Arizona  

Red,  at  Mangun,  Oklahoma  

Gunnison,  at  Whitewater,  Colorado                     .    . 

Pecos,  at  Carlsbad,  New  Mexico  

Pecos,  at  Dayton,  New  Mexico  

Rio  Grande,  at  El  Paso,  Texas                           

Salt,  at  Roosevelt,  Arizona  

North  Platte,  at  Laramie,  Wyoming  

Many  streams  whose  waters  are  used  for  irrigation  carry  more 
or  less  material  in  suspension  which  becomes  a  very  important  factor 
in  maintaining  the  fertility  of  the  soil.  The  amount  of  sediment 
carried  in  suspension  by  various  streams  is  given  in  the  above 
table. 

Composition  of  River  Sediments. — Many  river  sediments  have 
been  analyzed  in  the  United  States,  in  Europe,  and  in  Egypt.  The 
results  show  that  river  muds  are  somewhat  richer  in  the  essential 
plant  food  elements  than  the  ordinary  fertile  soils  from  which  the 
water  comes.  It  has  been  estimated  by  Forbes  that  the  market 
value  of  the  fertilizing  constituents  in  three  samples  of  Salt  TJivor 
mud,  to  the  acre-foot  of  water,  varied  from  $7.08  to  $25.51.2  When 
the  fertilizing  value  of  these  sediments  is  considered  in  connection 


IRRIGATION  263 

with  the  value  of  the  dissolved  materials,  one  of  the  great  advantages 
of  irrigation  is  made  evident.  By  this  addition  of  "plant  food  from 
year  to  year  cropping  may  continue  indefinitely  without  depleting 
the  soil.  Some  streams  are  exceptions  to  this  rule,  however. 

Time  of  Irrigation. — The  irrigation  of  crops  may  take  place  at 
various  times,  depending  upon  the  crop  grown  and  the  object  to 
be  accomplished.  Theoretically  the  soil  should  be  supplied  with 
just  sufficient  water  to  maintain  optimum  conditions  for  growth 
and  maturity.  This  is  a  condition  to  he  desired,  whether  ever  at- 
tained or  not;  however,  this  is  rarely  possible,  since  the  supply  of 
water  frequently  runs  so  low  that  during  part  of  tbe  growing 
season  it  is  not  adequate  for  the  purpose. 

Irrigation  may  be  done  either  when  the  crop  is  not  growing,  in 
the  fall,  winter  or  early  spring,  or  when  the  crop  is  growing  during 
the  summer.  In  the  former  case  the  ohject  is  to  obtain  the  water 
when  the  demand  for  it  is  not  so  great  and  store  it  in  the  soil  for 
use  the  next  season.  It  may  he  done  immediately  after  harvest  and 
from  then  till  spring.  Winter  irrigation  is  not  advisable  when  the 
soil  is  frozen,  as  much  of  the  water  may  he  lost,  but  where  (he  win- 
ters are  mild  it  may  be  practiced  to  good  advantage. 

Alfalfa  and  wheat  should  not  he  flooded  during  the  winter  in 
cold  climates. 

Irrigation  water  may  be  applied  early  in  the  spring  to  save  some 
of  the  water  of  the  spring  floods  caused  by  the  melting  snows  of 
the  mountains.  This  would  be  largely  lost  unless  reservoirs  have 
been  built  to  store  it  for  summer  use.  The  time  and  frequency  of 
irrigation  depend  upon  the  crop.  In  Arizona  orchards  receiving 
fall  and  winter  irrigations  have  produced  well  without  any  further 
application  of  water.  Alfalfa  should  be  irrigated  several  times,  a 
few  days  before  cutting  and  again  soon  after  the  crop  has  been 
harvested.  Wheat  and  other  small  grains,  beans  and  peas  if  planted 
in  a  soil  well  filled  with  moisture  need  little  or  no  irrigation  till 
flowering  time.  This  permits  a  good  root  system  to  develop.  Early 
irrigation  lessens  the  proportion  of  grain  to  straw. 

Amount  of  Water  to  Apply. — As  a  general  rule  the  more 
water  that  is  applied  to  a  soil,  within  practical  limits,  the  larger 
amount,  of  dry  matter  it  produces.  The  problem  is  not  to  go  beyond 
the  point  of  most  profitable  returns.  Tin's  point  has  not  yet  been 
determined.  Tt  is  very  difficult  of  determination,  since  it  varies 
with  the  crop,  the  soil,  rainfall  and  other  conditions. 

Usually  more  water  is  applied  than  is  necessary  and  certainly 


264 


SOIL  PHYSICS  AND  MANAGEMENT 


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IRRIGATION 


265 


more  than  is  economical.  In  the  table  the  additional  amounts  of 
water  applied  gave  an  increase  in  the  total  dry  matter  produced, 
yet  the  increase  of  dry  matter  per  acre-inch  of  water  decreased. 
The  increase  obtained  was  not  always  profitable.  It  will  be  noted 
that  the  yield  of  wheat  is  37.8  bushels  per  acre  where  five  inches 
of  water  were  applied,  while  7.5  inches  gave  a  yield  of  41.5  bushels, 
or  an  increase  of  1.5  bushels  per  acre-inch.  When  2.5  inches  more 
were  added  the  increase  was  0.8  bushel  per  acre-inch,  and  when  five 
inches  more  were  applied  the  increase  was  0.4  bushel  per  acre-inch. 
The  next  ten  inches  gave  less  than  one-tenth  of  a  bushel  increase 
per  acre-inch.  It  is  very  evident  that  the  point  of  profitable  appli- 
cation of  water  has  been  passed. 

The   Producing   Power  of  30  Acre-Inches    When  Applied  to  Different  Areas 

of  Land  4 

30  Acre-inches  spread  over 


Crop 

One  acre 
30  inches 
deep 

Two  acres 
15  inches 
deep 

Three  acres 
10  inches 
deep 

Four  acres 
7.5  inches 
deep 

Six  acres 
5  inches 
deep 

Wheat: 
Grain,  bushels       

47.51 

91.42 

130.59 

166.16 

226  86 

Straw,  pounds 

4533 

7908 

10356 

13204 

17916 

Corn: 
Grain,  bushels         .  .  . 

97.12 

187.86 

268.56 

316.56 

Stover    pounds 

10390 

10558 

1S021 

28756 

Timothy: 
Hay,  pounds 

6054 

7688 

11739 

11928 

Sugar  beets: 
Tons  

20.82 

38.90 

55.89 

64.84 

82.68 

Potatoes  : 
Bushels                      .    . 

195 

373 

456 

f>44 

69  1 

Alfalfa: 
Ha\'i  pounds             .    .  . 

8840 

15093 

266.r>3 

The  one  object  to  be  kept  in  mind  in  irrigation  is  to  grow  the 
maximum  amount  of  dry  matter  with  an  acre-inch  of  water.  Ex- 
periments show  that  10  to  20  inches  is  the  most  practicable  amount 
to  apply.  Larger  amounts  lower  the  quality  of  the  grain  and  do  not 
give  proportionate  increases. 

The  above  table  shows  the  value  of  small  applications  over  more 
extensive  areas  in  comparison  to  the  same  application  on  smaller 
areas. 


266 


SOIL  PHYSICS  AND  MANAGEMENT 


Returns  from  Sugar  Beets  Where  80  Acre-Inches  are  Distributed  Over  Different 

Areas  * 


30  acre-inches 
spread  over 

Inches  of 
water  on 
each  acre 

Yield  of 
beets  per 
acre  (tons) 

Total 
yield  of 
beets  (tons) 

Price 
per  ton 

Gross 
returns 

Total 
cost 

Net 

returns 

1  acre  

30.0 

21.0 

21 

$5 

$105 

$  60 

$  45 

2  acres  

15.0 

19.5 

39 

5 

195 

120 

75 

3  acres  

10.0 

18.6 

56 

5 

280 

180 

100 

4  acres  

7.5 

16.3 

65 

5 

325 

240 

85 

From  the  above  table  it  will  be  seen  that  30  acre-inches  spread 
over  three  acres  gives  the  greatest  net  returns.  The  results  of  the 
Utah  Station  indicate  that  where  the  annual  rainfall  is  12  to  15 
inches  an  application  of  10  to  20  inches  is  sufficient  for  ordinary 
crops,  and  the  best  amount  lies  near  the  lesser  quantity.  Dr.  F.  II. 
Newell  is  of  the  opinion  that  12  acre-inches  is  sufficient  to  produce 
good  crops  of  all  kinds  except  alfalfa  and  a  few  other  similar  crops. 

Loss  of  Water  from  Canals. — It  is  everywhere  agreed  that  a 
very  large  part  of  the  water  diverted  from  streams  is  lost  before  it 
reaches  the  place  where  it  is  to  be  applied  to  the  land.  It  is  esti- 
mated that  5.77  per  cent  of  the  water  is  lost  for  each  mile  of  canal 
through  which  it  is  carried.  This  means  that  all  the  water  would 
be  lost  in  17  miles.  The  loss  is  caused  by  evaporation  and  seepage. 
The  canals  pass  over  all  kinds  of  soil,  both  porous  and  impervious. 
Large  amounts  are  lost  where  the  canal  passes  over  gravelly  or 
sandy  soil.  This  seepage  water  not  only  does  very  little  good,  but 
in  many  cases  does  much  harm  by  causing  the  water  table  to  rise 
injuriously  near  the  surface  and  also  brings  up  the  alkali.  Some 
expedients  are  used  to  diminish  this  loss.  The  soil  is  sometimes 
puddled  by  dragging  chains  in  the  bottom  of  the  canals  (Fig.  119), 
thus  rendering  the  soil  less  pervious.  The  bottom  and  sides  of 
canals  are  sometimes  covered  with  crude  oil  to  lessen  leakage.  The 
large  canals  are  sometimes  lined  with  concrete  (Fig.  114),  which 
limits  the  loss  to  the  evaporation.  Even  fine  soil  constituents,  such 
as  clay  or  silt,  have  been  used  for  lining  the  canals  to  render  them 
less  pervious.  This  is  accomplished  in  part  by  the  sediment  carried 
by  water. 

It  is  estimated  that  in  India  the  loss  is  from  20  to  75  per  cent 
from  the  canals.  The  investigations  of  the  Department  of  Agri- 
culture in  this  country  show  that  nearly  GO  per  cent  of  the  water  is 
lost  between  the  head  gates  and  the  laterals  and  a  considerable  por- 
tion of  the  remaining  40  per  cent  is  lost  before  it  reaches  the  land 


IRRIGATION  207 

to  be  irrigated.  Fortier  says  that  less  than  one-third  of  the  water 
diverted  from  the  streams  is  actually  used  by  the  crops. 

The  Duty  of  Water. — "  The  duty  of  water,"  a  term  long  since 
coined,  means  the  quantity  of  water  needed  to  mature  crops.  It 
may  be  expressed  in  various  ways.  Sometimes  the  duty  of  water 
is  expressed  as  the  number  of  pounds  of  water  required  to  produce 
one  pound  of  the  dry  matter  of  the  crop;  under  other  conditions, 
as  the  depth  of  water  over  the  field  required  during  the  growing 
season  to  produce  the  crop. 

More  commonly,  however,  the  duty  of  water  is  expressed  as  the 
number  of  acres  that  may  be  irrigated  by  a  definite  quantity  of 
water,  say  a  second-foot,  flowing  continuously  through  the  growing 
season.6  A  second-foot  of  water  means  that  a  cubic  foot  of  water  is 


Fio.   119. — Chains  for  puddling  the  mud  of  canals  to  prevent  seepage. 

delivered  each  second  and  may  be  easily  reduced  to  acre-feet  or  acre- 
inches,  since  at  this  rate  an  acre-inch  will  be  delivered  each  hour. 

The  absolute  duty  of  water  is  the  total  amount  that  the  crop 
receives  by  irrigation,  by  rainfall,  and  that  contained  in  the  soil. 
It  is  expressed  as  acre-inches.  The  net  duty  of  water  is  the  amount 
actually  delivered  to  the  farmer  through  his  head-gate. 

One  second-foot  serves  to  irrigate  from  '2~>  to  over  300  acres 
during  the  growing  season.  An  average  is  from  7.1)  to  100  acres.  Tf 
the  acreage  irrigated  by  a  second-foot  is  small,  the  duty  of  water  is 
low,  while  if  the  acreage  is  large  the  duty  is  high. 

The  duty  of  water  varies  with  several  factors:  (1)  The  rainfall 
varies  in  irrigated  regions  from  almost  nothing  to  .10  or  10  inches. 
The  acreage  irrigated  bv  a  second-foot  will  necessarilv  vary  with 
the  rainfall.  (?)  Soils  that  are  quite  porous  will  require  more 
water  for  the  crop  than  the  less  pervious  ones,  since  much  will 
be  lost  by  percolation.  Even  hardpan  soils  require  more  water  than 


268 


SOIL  PHYSICS  AND  MANAGEMENT 


those  of  uniform  texture.  (3)  Different  crops  require  different 
amounts  of  water.  Forage  crops,  especially  alfalfa,  require  more 
water  than  cereals.  (4)  A  fertile  soil  requires  less  water  than  a 
run-down  soil.  (5)  The  amount  of  water  required  depends  to  some 
extent  upon  the  amount  of  water  applied  and  the  means  taken  to 
conserve  it. 

Duty  of  Water  in  Different  Countries. — Irrigation  is  prac- 
ticed on  all  continents.  The  duty  of  water  in  Egypt  is  115  acres 
for  cotton  and  other  dry  crops  and  60  acres  for  rice.  This  is  for  an 
irrigation  period  of  75  days.  In  southern  Africa,  where  the  annual 


A  -%l  . 

Fia.   120. — Rectangular  weir. 


rainfall  is  from  20  to  35  inches,  the  duty  of  water  is,  for  vegetables 
100  to  180  acres;  for  cereals  140  to  200  acres;  for  sugar  cane  50  to 
75  acres.  In  India  the  duty  from  June  to  October  is  80  to  170 
acres,  while  from  November  to  March  it  is  90  to  200  acres.  Under 
some  canals  160  acres  have  been  adopted  as  the  normal  duty. 

In  Europe  the  duty  is  somewhat  higher  than  in  most  countries, 
because  of  higher  rainfall.  The  average  for  Spain  is  172  acres, 
while  that  for  France,  Spain  and  Italy  is  239  acres.  Investigations 
in  North  America  show  that  the  duty  of  water  is  about  100  acres 
for  an  irrigation  sea-son  of  90  days. 

Measurement  and  Distribution  of  Water. — Since  water  is  a 
thing  of  such  great  value  in  irrigation,  its  measurement  becomes  a 


IRRIGATION 


269 


necessity  to  protect  the  farmer  who  is  the  purchaser  or  consumer 
and  the  company  that  furnishes  the  water.  Many  devices  have  been 
used,  hut  the  most  common  ami  most  satisfactory  is  the  weir  or 
overfall  (Fig.  120).  The  weir  should  be  installed  where  the  canal 
is  long,  straight  and  level.  A  box  is  placed  in  the  canal  so  that  all 
water  must  flow  through  it.  A  board  with  a  notch  is  placed  in  the 
box  and  across  the  stream.  This  notch  may  be  several  inches  or  even 


Flo.    121. — Trapezoidal  or  Cippolctti  weir,  Hhowing  method  of  dividing  the  stream.      (Utah 
Agricultural  Experiment  .Station.) 

several  feet  long  and  the  depth  of  water  flowing  through  this  may 
be  easily  measured  and  the  total  amount  determined  from  a  table. 
These  notches  may  be  either  rectangular,  trapezoidal,  or  triangular. 
The  trapezoidal  is  coming  into  most  general  use. 

For  purposes  of  distribution  to  different  laterals  the  streams 
are  frequently  divided  at  the  overfall  bv  placing  a  hoard  with  a 
sharp  edge  so  as  to  separate  the  stream  into  two  or  more  parts  (Fig. 
121).  Each  part  is  then  conducted  off  in  a  separate  lateral  to  the 
region  desired. 


270 


SOIL  PHYSICS  AND  MANAGEMENT 


Methods  of  Irrigation. — The  manner  of  applying  water  to 
soils  determines  to  a  large  extent  the  influence  it  has  both  upon 
the  plant  and  soil  as  well  as  the  effectiveness  of  the  water  itself. 

In  arid  regions  two  general  systems  of  irrigation  are  followed, 
flooding  and  furrowing,  each  of  which  has  its  advantages  under 
certain  conditions.  The  determining  factors  are  (1)  the  character 
of  the  soil,  (2)  the  amount  of  water  per -unit  of  time  or  "head/2 
(3)  the  contour  or  lay  of  the  land,  and  (4)  the  kind  of  crop. 

(a)   Flooding. — A  common  method  for  applying  water  is  by 


Fro.   122. — Basin  or  check  system  of    irrigating  orchards.    Principles  of  Irrigation  Practice, 
Widtsoe.      (Courtesy  Macmillan  Company.) 

flooding  the  entire  area.  This  requires  that  the  land  shall  be  prac- 
tically flat  and  the  soil  one  that  does  not  erode  badly  nor  bake 
upon  drying.  Heavy  soils  are  best  adapted  to  this  method,  so  that 
when  the  large  volume  of  water  is  turned  on  the  soil  will  not  wash. 
If  the  volume  of  water  is  too  small  it  will  sink  into  the  soil  before  it 
reaches  the  other  side  of  the  field.  Alfalfa,  pasture  and  meadow 
land  and  wheat  and  other  small  grains  may  be  successfully  irrigated 
in  this  way.  Three  principal  modifications  of  this  method  are 
flooding  closed  fields,  flooding  open  fields  and  basin  flooding.  The 
closed-field  flooding  or  check  flooding,  as  it  is  sometimes  called,  is 


IRRIGATION 


271 


whore  a  levee  or  dike  is  built  around  the  field  and  into  which  the 
water  is  turned  and  left  till  it  is  all  absorbed.  rl  his  is  a  common 
practice  in  China  and  Japan.  In  open  field  flooding  a  canvas  dam 
is  placed  in  the  ditch  and  the  water  forced  to  run  over  the  banks 
of  the  ditch  into  the  field.  A  moderate  slope  permits  it  to  run 
slowly  over  the  field  where  the  surplus  water  runs  into  another 
ditch  at  the  lower  side. 

Basin  flooding  is  practiced  in  orchards,  the  levee  being  thrown 
up  so  as  to  occupy  the  space  allotted  to  each  tree.  The  water  is  al- 
lowed to  enter  the  enclosure  and  left  till  it  is  absorbed  (Fig.  12'2). 
Dirt  is  piled  around  the  base  of  the  tree  so  the  bark  will  not  get 
wet.  This  method  is  gradually  passing  out  of  use. 


Fio.   123. — Irrigating  potatoes  by  furrows.     I".  S.  Reclamation  Service. 

(b)  Furrow  Irrigation. — The  furrow  method  of  irrigation  is 
one  of  the  most  common  and  for  most  conditions  one  of  the  best 
methods  practiced.  Small  furrows  lead  from  the  supply  ditch  and 
the  water  is  absorbed  by  the  soil  (  Fig.  1  :>.'{).  The  furrows  are  from 
five  to  ten  inches  deep  and  from  three  to  eight  feet  apart,  the  dis- 
tance depending  upon  the  soil  and  the  crop.  By  this  method  the 
irrigator  may  control  the  quantity  of  water  and  a  comparatively 
small  amount  may  be  spread  over  a  large  area  of  land.  Onlv  a 
small  amount  of  the  soil  becomes  wet.  so  that  injury  from  puddling 
is  not  imminent.  The  furrows  may  soon  be  covered  and  thus  reduce 
evaporation,  preventing  or  retarding  the  rise  of  alkali.  Tt  is  very 
difficult  to  obtain  uniform  distribution,  due  to  the  difference  in  the 
absorbing  power  of  the  soil  or  length  of  furrow  or  both.  This 


272 


SOIL  PHYSICS  AND  MANAGEMENT 


method  is  specially  adapted  to  inter-tilled  crops,  such  as  corn  and 
potatoes,  and  is  used  extensively  for  cereals,  alfalfa,  and  orchards. 

(c)  Sub-Irrigation. — The  method  of  sub-irrigation  is  prac- 
ticed only  to  a  very  limited  extent  because  of  the  great  initial  cost 
making  it  almost  prohibitive.  Iron,  concrete  or  wooden  pipes  may 
be  used,  but  digging  the  trenches  for  placing  these  is  expensive. 
The  roots  clog  the  openings  and  in  time  impair  the  usefulness  of 
the  system. 

A  form  of  natural  sub-irrigation  is  practiced  in  the  West  where 


Fio.  124. — Method  of  irrigating  by  overhead  sprays.  Adapted  to  small  fruits  and 
vegetables  in  humid  areas.  (Fortier's  Use  of  Water  in  Irrigation.)  (Courtesy  McGraw- 
Hill  Book  Company.) 

the  soil  is  sufficiently  porous  so  that  no  underground  pipes  are 
necessary.  Former  irrigation  has  brought  the  water  table  near 
the  surface,  and  now  the  object  to  be  accomplished  is  to  keep  the 
water  table  sufficiently  near  the  surface  so  that  capillary  water  from 
it  will  supply  the  crops.  An  impervious  stratum  is  necessary  at  a 
depth  of  a  few  feet.  A  tract  of  60.000  acres  is  irrigated  in  this  way  in 
the  upper  Snake  River  Valley,  Idaho.  Parts  of  the  San  Luis  Valley, 
Colorado,  are  irrigated  in  the  same  manner.  The  ditches  are  from 
50  to  250  feet  apart. 

(d)  Surface  Sprinkling  and  Overhead  Sprays. — This  method 
is  adapted  only  to  small  areas  and  is  one  of  the  most  expensive  as 


IRRIGATION  273 

well  as  ineffective  ways  of  applying  water.  It  is  distributed  under 
pressure  through  pipes,  the  water  escaping  by  means  of  nozzles  or 
by  small  openings.  It  is  used  principally  to  supplement  the  rain- 
fall (Fig.  124)  in  humid  regions  where  crops  of  high  value,  such 
as  vegetables  and  small  fruits,  are  grown.  Usually  the  application 
is  sufficient  to  penetrate  only  to  a  slight  depth,  hence  it  soon  evapo- 
rates. It  has  a  tendency  to  produce  shallow  rooting  of  the  plants. 
The  method  has  the  advantage  of  easy  control,  little'  waste  land, 
and  may  be  used  on  very  uneven  land. 

Cultivation  After  Irrigation. — Where  possible  the  irrigated 
land  should  be  cultivated  as  soon  as  the  soil  is  in  proper  condition. 
The  loss  by  evaporation  following  irrigation  is  enormous,  especially 
where  no  crop  is  on  the  land  large  enough  to  shade  it.  The  Utah 
Station  found  that  where  land  was  not  cultivated  till  seven  days 
after  irrigation  the  loss  of  water  by  evaporation  was  1.45  inches  or 
1G4  tons  per  acre,  while  14  days  gave  a  loss  of.  l.!K>  indies  or  21!) 
tons  per  acre,  and  21  days  gave  a  loss  of  2.7  inches  or  :><>T  tons.  The 
cultivation  should  be  as  deep  as  possible  under  the  circumstances. 
As  the  result  of  an  experiment  a  loss  of  1.75  inches  occurred  in 
28  days  where  there  was  no  mulch.  When  a  layer  of  dry  granular 
soil  three  inches  thick  was  placed  upon  the  surface  the  evaporation 
was  reduced  to  0.78  of  an  inch  or  57.7  per  cent,  while  a  ten-inch 
mulch  practically  stopped  evaporation. 

Crops  for  Irrigated  Lands. — Practically  all  crops  adapted  to 
the  climate  will  grow  under  irrigation.  Some  require  more  water 
than  others,  but  this  is  easilv  adjusted  by  the  applications  of  water. 
(Fig.  125.) 

Cereals. — Wheat. — The  best  cereal  under  irrigation  is  wheat. 
While  it  is  primarily  a  crop  for  dry-land  agriculture,  yet  it  yields 
well  when  irrigated  and  is  a  good  crop  to  fit  in  with  rotations  used 
on  irrigated  lands,  and  is  grown  quite  extensively.  The  amount  of 
water  required  by  wheat  depends  upon  the  perviousness  of  the  soil, 
but  in  a  deep,  fertile1,  well-tilled  soil  12  inches  will  be  sullicient. 
The  Utah  Station  found  that  an  application  of  7.5  inches  of  water 
gave  11.5  bushels,  10  inches  gave  i:?.5  bushels,  and  15  inches  gave 
45.7  bushels  per  acre. 

Oafs. — The  growing  of  oats  on  irrigated  land  probably  will 
never  become  very  extensive,  although  it  will  be  used  t<>  some  extent 
to  give  variety  in  rotations.  It  produces  well  and  requires  about  the 
same  amount  of  water  as  wheat. 

Ttarlcii. — The  barley   crop   is  a   valuable  one  under   irrigation. 
18 


274 


SOIL  PHYSICS  AND  MANAGEMENT 


producing  well  and  requiring  a  less  amount  of  water  than  other 
cereals.  After  an  application  of  7.5  inches  of  water  little  increase 
was  obtained  with  more.  The  barley  produced  under  irrigation  is 
of  better  quality  than  that  produced  on  dry  land. 


FIQ.  125. 


FIG.  126. 

Fio.  125. — Mallin  Ranch,  Salt  River  Project,  Arizona. 
FIG.   126. — Alfalfa  field.     Yuma  Project,  Arizona. 


)U.  S.  Reel  a 
j  Servic 


Corn  produces  more  dry  matter  in  proportion  to  the  water 
applied  than  almost  any  other  crop.  Tt  is  not  yet  grown  exten- 
sively under  irrigation,  but  its  area  is  increasing,  especially  in 
regions  where  stock  raising  is  a  prominent  industry.  Tt  has  a 


IRRIGATION  275 

longer  irrigation  period  than  small  grains,  therefore  requires  more 
water.  Cultivation  alter  each  irrigation,  is  very  essential.  An  appli- 
cation of  25  inches  gave  !)!>.!  bushels  per  acre  at  the  Utah  Station. 

Rice  is  a  crop  that  is  grown  under  humid,  semi-tropical  con- 
ditions, but  irrigation  or  flooding  is  necessary  The  check  system  is 
used.  Levees  are  thrown  up  sufficiently  high  to  retain  a  layer  of 
water  to  a  depth  of  three  to  ten  inches.  The  water  is  nearly  always 
applied  by  pumping  from  wells  or  canals. 

Forage  Crops. — Alfalfa  is  not  only  the  most  important  crop  for 
forage  purposes,  but  it  is  the  most  valuable  of  all  crops  grown 
under  irrigation  (Fig.  12(>).  Its  value  is  enhanced  by  the  fact  that 
it  is  a  nitrogen  gatherer  and  actually  builds  up  the  soil  during  its 
growth. 

Water  may  be  applied  by  furrows,  flooding,  or  by  checking. 
When  water  is  abundant  flooding  is  the  method  used.  If  the  soil 
bakes  or  tends  to  run  together,  the  furrow  method  is  preferable.  In 
this  case  the  land  is  marked  off  or  furrowed  immediately  after  seed- 
ing and  the  furrows  become  permanent.  Alfalfa  requires  somewhat 
more  water  than  cereals,  and  18  to  24  inches  should  be  applied. 
Fortier  found  that  30  acre-inches  applied  to  one  acre  produced 
14,400  pounds  of  hay.  while  when  the  same  amount  of  water  was 
applied  to  five  acres  (54,100  pounds  were  produced. 

If  seed  is  to  be  produced  but  little  water  should  be  applied  to 
the  growth  that  is  to  produce  the  seed. 

Olhcr  Forage  Crop*. — Timothy,  orchard  yraxs  and  bronic  ///v/.w 
are  crops  that  thrive  under  irrigation,  but  are  very  inferior  to 
alfalfa  in  this  respect.  Clover  does  well  under  irrigation,  but  pro- 
duces much  less  hay  than  alfalfa. 

The  sugar  beet  is  one  of  the  most  profitable  of  irrigated  crops. 
It  prefers  a  deep  clay  loam  soil  and  dry  summers.  Three  to  five 
irrigations  are  sufficient  and  on  some  soils  only  t\vo  are  deemed 
necessary.  From  four  to  six  inches  are  applied  at  each  irrigation. 

Potatoes  are  a  very  important  crop  on  irrigated  land.  Their 
water  requirements  are  somewhat  like  sugar  beets.  The  furrow 
method  is  practiced.  Fifteen  to  twenty-four  inches  of  water  should 
I'e  sufficient. 

Peas,  beans,  melons,  tomatoes,  onions,  cotton,  and  manv 
other  crops  may  be  grown  very  successfully  under  irrigation. 

Fruits  of  nearly  all  kinds  may  he  grown  where  climatic  con- 
ditions are  right. 

Irrigation  in  Humid  Climates. — An   annual   precipitation  of 


276  SOIL  PHYSICS  AND  MANAGEMENT 

30  inches  or  more  gives  sufficient  moisture  for  producing  fair  crops 
of  nearly  all  kinds  if  the  rainfall  is  distributed  properly.  Drouthy 
periods  are  quite  common.  At  Columbia,  8.  C.,  02  fifteen-day 
periods  with  less  than  one  'inch  of  rainfall  during  the  growing 
season,  April  to  October,  occurred  from  1900-11)09.  At  Vineland, 
N.  J.,  40  periods,  at  Oshkosh,  Wis.,  27  periods,  and  at  Ames,  Iowa, 
23  similar  periods  occurred  during  the  same  time.  At  the  Illinois 
Station  from  1906-1915  there  were  49  periods  of  drouth  15  days 
long,  while  16  were  more  than  25  days  and  six  more  than  30  days 
in  length. 

While  this  uneven  distribution  indicates  that  irrigation  might 
be  practiced  during  some  years  with  profit,  it  is  very  doubtful,  how- 
ever, whether  it  will  ever  be  profitable  for  the  ordinary  cereals.  A 
four-year  rotation  7  of  corn,  oats,  and  clover  was  followed  on  brown 
silt  loam,  the  common  prairie  soil  of  the  corn  belt,  for  10  years. 
Without  irrigation  a  ten-year  average  yield  was  43.5  bushels,  while 
adjoining  plots,  irrigated  when  necessary,  gave  a  yield  of  49.9 
bushels  per  acre,  an  increase  of  6.4  bushels.  During  the  dry  seasons 
of  1911,  1913  and  1914  the  yield  of  corn  averaged  32.3  bushels 
without  and  50.8  bushels  with  irrigation,  an  iiicrease  of  18.5  bushels. 
Even  with  this  large  increase  for  dry  seasons  the  average  increase 
is  insufficient  to  pay  for  irrigation. 

Irrigation  of  truck  and  some  fruit  crops,  without  doubt,  could 
be  practiced  profitably,  and  in  general  the  more  valuable  the  crop 
the  more  profitable  irrigation  becomes.  Strawberries  and  bush 
fruits  respond  well  to  irrigation,  both  with  a  finer  quality  of  fruit 
and  a  longer  fruiting  period. 

i 
QUESTIONS 

1.  Upon  what  factors  does  the  profit  from  irrigation  depend? 

2.  Why  is  the  irrigable  area  so  limited? 

3.  Look  up  some  of  the  projects  given  in  the  table  on  page  257. 

4.  What  are  the  sources  of  irrigation  water? 

5.  What  preparation  is  necessary  before  the  land  can  be  irrigated? 

6.  Why  sliould  not  saline  water  be  used  for  irrigation  ? 

7.  Is  the  sediment  carried   in  ^suspension   detrimental  or   not?      If  bene- 

ficial, why? 

8.  What  are   the   advantages   and   disadvantages   of   irrigation   when    the 

crop  is  not  growing? 

9.  May  too  much  water  be  used  in  irrigation  ? 

10.  What  is  meant  by  the  "  duty  of  water"? 

11.  What  is  a  second-foot  of  water? 

12.  What  is  the  absolute  duty  of  water?     How  is  it  expressed? 

13.  How  much  will  a  second-foot  irrigate? 

14.  What  causes  this  variation? 


IRRIGATION  277 

15.  How  much  water  should  bo  applied  to  a  crop? 

10.  Study  carefully  the  proportionate  increase  of  yield  for  increased  appli- 
cation of  water  in  the  table  on  page  2t>4. 

17.  Compare  the  yield  per  acre  where  7.5  inches  were  applied  with  that  for 

30  inches.     Did  the  large  application  pay? 

18.  How  is  water  lost  from  the  irrigation  canals? 

19.  What  is  the  significance  of  this  loss? 

20.  How  i's  this  loss  prevented  ? 

21.  How  is  the  water  measured? 

22.  What  are  the  advantages  and  objections  to  surface  sprinkling? 

23.  What  is  check-flooding? 

24.  Give  advantages  of  furrow  irrigation. 

25.  Why  should  the  irrigated  land  lie  cultivated  soon  after  irrigation? 

26.  Under  what  conditions  is  irrigation  in  humid  climates  profitable? 

REFERENCES 

1  Widtsoe,  J.  A.,  Principles  of  Irrigation  Practice,  1911,  p.  !)G. 

2  Forbes,  K.  H.,  Bulletin  44,  Arizona  Station,  The   Kivcr  Irrigating  Waters 

of  Arizona,  1902,  p.  100. 

3  Widtsoe,  J.  A.,  Bulletin  110,  Utah  Station,  The  Production  of  Dry  Matter 

with  Different  Quantities  of  Irrigation  Water,   1912.     Widtsoe.  J.  A., 
and   Merrill,   L.   A.,   Bulletin    117,   Utah   Station,  The  Yields  of  Crops 
with  Different  Quantities  of  Irrigation  Water,  1912. 
'Bulletin  117,  Utah,  Op.  Cit.,  p.  115. 

5  Widtsoe,  J.  A.,  Principles  of  Irrigation  Practice,  1911,  p.  337. 

6  Widtsoe,  J.  A.,  Principles  of  Irrigation   Practice.  1911.  p.  331. 

7  Mosier,  .F.   (',.,  and  (iustafson,   A.    F..   Bulletin    181,   Illinois   Station,   Soil 

Moisture  and  Tillage  for  Corn,  1915. 

General  References. — Fortier,  Samuel,  Yearlwok  U.  S.  D.  A..  Methods 
of  Applying  Water,  1909,  p.  293.  McLaughlin,  W.  W.,  Farmers'  Bulletin 
399,  I'.  S.  I).  A.,  Irrigation  of  (Jrain,  1910.  Welsh,  J.  S..  Bulletin  74.  Idaho 
Station,  Irrigation  Practice,  1914.  Hoed  ing,  F.  W..  Farmer*'  Bulletin  392. 
U.  S.  1).  A.,  Irrigation  of  Sugar  Beets,  1910.  Newell,  F.  H.,  Irrigation, 
1906. 


CHAPTER    XXH 

ALKALI  LANDS  AND  THEIR  RECLAMATION 

ALKALI  lands  are  found  in  all  regions  of  deficient  rainfall.  They 
usually  occur  where  the  rainfall  is  less  than  20  inches,  but  in  India 
alkali  lands  exist  even  with  a  rainfall  of  28  inches.  The  effective- 
ness of  rainfall  in  removing  alkali  depends  upon  its  character.  If 
the  rainfall  comes  in  very  heavy  showers,  as  is  the  case  in  India, 
much  will  run  off  the  surface  without  entering  the  soil,  and  hence 
will  do  little  toward  removing  the  alkali.  A  small  rainfall  coming 
as  gentle  showers  so  that  it  will  enter  the  soil  will  he  more  effective. 

The  effect,  too,  of  the  rainfall  depends  somewhat  upon  the  char- 
acter of  the  soil.  Rainfall  will  penetrate  a  loose,  sandy  loam  soil 
much  more  readily  than  a  clay.  Hence,  under  the  same  rainfall  a 
clay  soil  or  a  clay  loam  soil  may  contain  alkali,  while  the  sandy  loam 
or  sand  would  he  free  fron^  it.  The  amount  of  evaporation,  too, 
plays  a  somewhat  important  part  in  the  amount  present.  Under 
conditions  of  great  evaporation  the  alkali  may  be  brought  to  the  sur- 
face, while  with  less  evaporation,  as  in  a  more  northern  climate,  the 
alkali  would  not  be  troublesome  at  all. 

Alkali  does  not  usually  occur  in  hill  lands,  although  in  small 
level  valleys  among  hills  alkali  may  be  found  in  considerable 
amounts.  It  occurs  abundantly  in  level  uplands  if  the  drainage  is 
in  any  way  interfered  with.  Alluvial  lands  frequently  contain 
alkali,  due  to  seepage  from  the  upland  and  also  from  the  water  of 
the  stream. 

The  Origin  of  Alkali. — In  the  decomposition  of  rocks  and  the 
further  decomposition  of  soil  material,  many  soluble  substances  are 
formed  which  may  not  be  leached  out  by  the  small  rainfall  of  the 
region  but  may  be  brought  to  the  surface  by  capillary  movement. 
Many  of  the  stratified  rocks  contained  much  salt,  due  to  the  fact 
that  they  were  formed  in  salt  or  brackish  waters.  When  these  be- 
came dry  land  the  salt  was  leached  out  later  and  carried  into"  tem- 
porary lakes.  This  accumulation  continued  and  ultimately  the 
lake  became  dry  and  a  deposit  of  alkali  was  left  (Fig.  127).  Salt 
springs  sometimes  occur,  the  waters  of  which  carry  considerable 
amounts  of  alkali  into  depressions,  where  they  may  accumulate  in 
large  quantities.  Whatever  the  'source  of  the  alkali,  its  existence 
278 


ALKALI  LANDS  AND  THEIR  RECLAMATION 


279 


is  usually  due  to  climatic  conditions.  It  naturally  results  from  a 
rainfall  insufficient  to  carry  soluble  material  out  of  the  soil,  which 
ultimately  becomes  so  impregnated  with  it  as  to  be  unproduc- 
tive (Fig.  128). 


Fi<;.    127.  —  RrttinninK 


•       .-.  • 
>.>t.      (T.  S.  Dopt.  of  Agriculture. 1 


' 


Fio.    12S.  —  Alkali  area  showinc  tho  nbsonro  of  vpRpfnti 


(T*.   S.   Drpt.   of   AKrirnltnro  .1 


280 


SOIL  PHYSICS  AND  MANAGEMENT 


Kinds  of  Alkali. — The  alkalies  of  arid  regions  are  commonly 
classified  as  black,  white,  and  brown.  The  black  consists  of  forms  of 
sodium  carbonate,  which  owe  their  name  to  the  color  produced  by 
the  solution  of  organic  matter  and  its  deposition  on  soil  particles 
during  evaporation.  There  are  at  least  two  forme  of  sodium  car- 
bonate included  in  the  black  alkali,  the  bicarbonate  (HNaC03)  and 
the  normal  carbonate  (Xa-jCOg). 

The  white  alkalies  are  composed  mainly  of  common  salt  ( NaCl ) 
and  sodium  sulfate  (Xa.,S04),  together  with  some  magnesium  sul- 
fate  (MgS04),  potassium  chloride  (KC1),  magnesium  chloride 
(MgCl2)  and  small  amounts  of  many  others.  The  brown  alkali 
consists  of  nitrates,  which  are  found  only  occasionally  in  damag- 
ing quantities.  Different  alkalies  usually  occur  as  mixtures  in 
various  and  indefinite  proportions.  A  careful  study  of  the  follow- 
ing table  shows  this  fact.  That  from  Kern  county,  number  one, 
contains  sodium  sulfate  principally,  but  with  some  potassium  sul- 
fate; number  two,  sodium  sulfate  and  chloride  with  some  nitrate; 
number  three  contains  sodium  and  potassium  carbonate  or  black 
alkali  largely;  while  four  is  a  mixture  of  sodium  sulfate,  chloride, 
carbonate,  and  nitrate. 

Percentage  Composition  of  Some  Typical  Alkali  Salts  l  (Hilgard) 


Kern 
County, 
California 

Meagher 
County, 
Montana 

Kittitas 
County, 
Washing- 
ton 

Tulare 
County, 
California 

Potash  

5.14 

1.18 

9.58 

1.76 

Soda  

36.99 

39.56 

45.59 

38.39 

Lime  

0.15 

2.86 

0.03 

Magnesia  

0.23 

1.31 

0.07 

Ferric  oxide  and  alumina  

0.30 

0.04 

Sulfuric  acid  

51.23 

34.97 

0.09 

13.20 

Chlorine  

0.29 

15.40 

0.99 

7.40 

Carbonic  acid  

0.23 

1.19 

34.93 

11.62 

Nitric  acid  

5.37 

10.50 

Phosphoric  acid  

0.09 

1.05 

1.05 

Silica  

1.34 

0.05 

0.82 

Organic  matter  and  water 

4.07 

1.29 

703 

1732 

The  amount  of  the  different  kinds  of  alkali  is  not  constant,  but 
changes  from  week  to  week. 

Effect  on  Physical  Condition  of  the  Soil. — The  black  alkali 
defloccnlates  the  soil,  producing  a  puddled  condition  due  to  the 
solution  of  the  organic  matter.  A  very  close  rearrangement  of  the 
particles  occurs  by  which  the  soil  becomes  impervious  to  water  and 
practically  untillable.  This  closer  arrangement  of  particles  de- 


ALKALI  LANDS  AND  THEIR  RECLAMATION 


281 


creases  the  volume,  producing  a  slight  depression  in  which  water  is 
likely  to  stand.  It  also  tends  to  form  tough  and  impervious  strata 
at  different  depths  in  the  soil. 

The  white  alkalies  have  no  injurious  effect  on  the  soil,  but,  on 
the  other  hand,  tend  to  produce  a  granular  character  that  is  very 
favorable  to  tilth. 

Vertical  and  Horizontal  Distribution. — The  distribution  of 
alkali  salts  is  very  irregular,  both  in  amount  and  kind.  The  follow- 
ing table  gives  the  vertical  distribution  in  one  place,  which  may  be 
somewhat  representative  of  most  alkali  areas.  There  is  a  zone  of 
greatest  concentration  at  about  the  depth  of  annual  percolation. 
This  zone  is  moved  downward  slightly  by  the  winter  and  spring 
rains  and  is  brought  upward  by  summer  evaporation.  In  heavy  soils 
it  will  be  nearer  the  surface  than  in  permeable  ones. 

Vertical  Distribution  of  Alkali  Before  and  After  Irrigation  at  Various  Depths, 
Tularc,  California.    Pounds  per  Acre  (Hilgard.-) 


Natural  soil,  uninitiated 

Bare  land,    irri- 
gated four  years 

0  to    6  inches  

May  3,  1895 

350 
460 
1350 
3160 
7530 
9550 
3380 
1300 

September,  1895 

420 
440 
1710 
4450 
7810 
8120 
1780 
690 

May,  1895 

12220 
7540 
6180 
3320 
1380 
760 
530 
500 

6  to  12  inches 

12  to  18  inches   

18  to  24  inches   

24  to  30  inches  

30  to  36  inches 

36  to  42  inches  

42  to  48  inches  . 

The  amount  of  alkali  in  an  area  or  even  in  a  small  field  varies 
almost  infinitely.  It  seems  to  move  from  place  to  place,  so  that  an 
area  with  abundant  alkali  may  in  short  time,  perhaps  not  over  a 
week  or  two,  have  much  less.  The  kind  of  alkali  varies  even  more 
than  the  quantity.  A  spot  of  black  alkali  may  change  to  white,  and 
vice  versa.  Low  places  in  irrigated  land  will  usually  contain  most 
alkali,  and  are  frequently  called  alkali  marshes. 

Effect  of  Irrigation  on  Rise  of  Alkali. — The  tendency  of  irri- 
. gation  is  to  increase  the  amount  of  evaporation  from  the  surface 
of  the  soil.  The  water  applied  enters  the  soil,  dissolves  the  salts  and 
carries  them  downward.  When  evaporation  begins  the  water  moves 
upward,  carrying  the  salts  with  it  and  depositing  them  at  the  sur- 
face. The  effect  of  successive  irrigations  and  the  excessive  evapora- 
tion that  follows  is  to  transfer  large  quantities  of  salts  to  the  sur- 


282 


SOIL  PHYSICS  AND  MANAGEMENT 


face  foot  of  soil.  This  is  spoken  of  as  the  "  rise  of  alkali "  and  the 
effect  is  to  ruin  the  land  for  ordinary  crops.  The  result  is  well 
shown  in  the  table  on  page  281,  where  the  surface  foot  contained 
19,7(>0  pounds,  while  the  same  depth  under  natural  conditions  con- 
tained 860  pounds. 

Amount  and  Composition  of  Salts  in  Alkali  Spot  from  Center  tb  Circumference, 
4  Feet  Apart  and  1  Foot  Deep 3 


Mineral  salts 

Center  of 
spot 

Four 
feet 

Eight 
feet 

Twelve 
feet 

Outer 
margin 

Potassium  sulfate  

6.70 

9.55 

11.92 

19.26 

13.95 

Sodium  sulfate  

19.84 

12.85 

23.72 

23.97 

16.96 

Magnesium  sulfate  .  . 

3.07 

.07 

.95 

2.05 

8.29 

Sodium  chlorid  

13.80 

23.73 

24.12 

24.23 

29.69 

Sodium  carbonate  

50.72 

50.96 

37.55 

35.49 

29.94 

Sodium  phosphate     .  .  • 

5.57 

2.88 

.87 

1.04 

Sodium  nitrate 

.30 

.87 

.13 

The  irrigation  canals  and  ditches  sometimes  pass  through  a 
rather  open  soil  that  permits  considerable  seepage.  It  is  estimated 
that  30  per  cent  of  the  water  taken  in  at  the  headgates  is  lost  by 
seepage  from  the  canals  themselves  and  another  third  is  gone  before 
it  is  used  for  irrigation. 

This  seepage  water  passes  through  the  soil,  dissolving  the  alkali, 
and  finally  both  water  and  alkali  come  to  the  surface  in  some  slightly 
lower  place  in  the  field.  This  alkaline  water  gives  rise  to  alkali 
marshes  which,  although  very  small  at  first,  gradually  increase  in 
size  until  much  of  the  land  is  affected.  The  "  rise  of  alkali "  has 
ruined  large  amounts  of  land  because  of  the  excessive  use  of  irriga- 
tion water.  The  desire  of  farmers  to  get  their  "  money's  worth  "  of 
water  has  hastened  their  ruin. 

Effect  of  Alkali  on  Plants. — A  few  plants  have  become  adapted 
to  growing  where  large  amounts  of  alkali  are  present  and  are  in- 
jured only  when  the  soil  becomes  very  strongly  alkaline.  There  are 
small  local  areas  where  the  alkali  is  sufficient  to  kill  all  vegetation. 
As  a  general  rule,  the^e  alkali-resistant  plants  are  not  of  much  eco- 
nomic importance. 

As  a  result  of  this  poisoning,  cultivated  plants  are  injured  to 
varying  degrees  (Fig.  129).  Where  the  alkali  is  very  strong  the 
plants  show  a  sickly  growth  and  finally  die  without  fruiting.  If 
less  in  amount  they  may  become  dwarfed  and  produce  rather 
scantily.  Affected  trees  show  a  scanty  leafage  with  small  fruiting. 

The  external  injury  done  to  plants  is  confined  to  a  narrow  zone 


ALKALI  LANDS  AND  THEIR  RECLAMATION 


283 


284 


SOILS  PHYSICS  AND  MANAGEMENT 


at  the  surface  of  the  soil  or  near  the  root  crown.  The  bark  is 
turned  to  a  brown  or  black  color  for  about  a  half  inch  and  may 
easily  be  peeled  off.  In  other  words,  the  plant  has  been  "  girdled." 
If  the  plant  does  not  die  it  becomes  unprofitable. 

The  roots  are  not  injured  perceptibly  to  any  depth,  as  a  general 
rule,  but  it  is  very  likely  that  the  entire  plant  is  poisoned  more  or 
less.  It  is  only  where  common  salt  is  very  abundant  in  the  subsoil 
that  the  deeper  roots  are  injured. 

Limit  for  Germination  and  Growth. — Germinating  plants  are 
most  sensitive  to  alkali,  hence  a  comparatively  small  amount  in  the 

Highest  Amount  of  Alkali  in  Which  Plants  Weie  Found  Unaffected* — Arranged 
from  Highest  to  Lowest.  Pounds  Per  Acre  Four  Feet  Deep 


Sulfatea 
(Glauber'ssalt) 

Carbonate 
(sal  soda) 

Chloride 
(common  salt) 

Total 
alkali 

Saltgrass  

44,000 

136,270 

70,360 

381,110 

Saltbush 

125,640 

18.560 

12,520 

156,720 

Alfalfa,  old 

102,480 

2,360 

110,320 

Sorghum  

61,840 

9,840 

9,680 

81,360 

Radish 

51,880 

8,720 

2,240 

62,840 

Sugar  beet  

52,640 

4,000 

10,240 

59,840 

Grapes  

40,800 

7,550     ' 

9,640 

45,760 

Onions 

5,810 

38,480 

Potatoes 

5,810 

38,480 

Barley  I  

12,020 

12,170 

5,100 

25.520 

Gluten  whea"t  .  . 

20,960 

3,000 

1,480 

24,320 

Oranges 

18,600 

3,840 

3,360 

21,840 

Wheat  

15,120 

1,480 

1,160 

17,280 

Apples  

14,240 

640 

1,240 

16,120 

Celery  

4,080 

9,600 

13,680 

Alfalfa,  young 

11,120 

13,120 

Rye.. 

9,800 

960 

1,720 

12.480 

Date  palrn  

5,500 

2,800 

8,328 

surface  soil  at  that  period  may  produce  very  serious  results.  As  an 
illustration,  young  alfalfa  will  not  stand  more  than  13.000  pounds 
of  alkali  hi  the  soil  to  a  depth  of  four  feet,  while  old  alfalfa  will 
flourish  where  nearly  ten  times  that  amount  exists,  and  this  is  true 
more  or  less  of  all  plants. 

In  the  growing  of  certain  crops  special  methods  are  employed 
for  reducing  the  amount  of  alkali  in  the  surface  soil  until  the  plant 
becomes  old  enough  to  resist  its  effect.  All  plants  are  not  equally 
injured  by  the  same  amount  of  alkali.  Some  will  grow  and  flourish 
where  others  will  die.  In  the  case  of  the  tussock  grass,  it  will  grow 
where  the  soil  to  a  depth  of  four  feet  contains  499,000  pounds  of 


ALKALI  LANDS  AND  THEIR  RECLAMATION  285 

alkali,  while  7000  or  8000  pounds  will  injure  the  lemon  tree.  The 
preceding  table  gives  the  highest  amount  of  alkali  in  which  plants 
were  found  unaffected. 

As  a  general  rule  plants. cannot  withstand  more  than  0.1  per  cent 
of  sodium  carbonate  or  1(1,000  pounds  in  a,  depth  of  4  feet,  O.^o  per 
cent  or  40,000  pounds  of  sodium  chloride  or  common  salt,  nor 
more  than  0.5  per  cent  or  80,000  pounds  of  sodium  sulfate.  If  the 
amounts  increase  to  any  extent  beyond  these,  the  plants  are  very 
seriously  injured. 

Utilization  and  Reclamation  of  Alkali  Lands, — The  large 
extent  and  great  value  of  alkali  lands  make  their  utilization  and 
reclamation  some  of  the  most  important  problems  in  irrigated 
regions.  While  a  great  many  methods  have  been  tried  with  partial 
success,  yet  the  removal  of  the  alkali  is  the  only  remedy  that  will 
permanently  reclaim  the  land.  It  may  be  well  to  notice  some  of 
the  more  or  less  temporary  expedients  for  utilizing  these  soils. 

1.  Growing    Alkali-Resistant    Crops. — All    plants    are    not 
equally  sensitive  to  alkali,  and  the  problem  here  is  to  find  the  crop 
of  highest  value  that  will  be  affected  least  by  the  salts.     The  salt 
grass  and  salt  bushes  grow  under  extreme  conditions  and  they  are 
of  considerable   value   for  forage.      Sweet   clover    (Melilot)    grows 
well  where  alkali  is  quite  abundant  and  furnishes  very  good  pasture 
and  forage  when  cut  early.     In  some  places  it  is  crowding  out  other 
plants.    For  gaining  the  requisite  knowledge,  the  kinds  and  amounts 
of  each  alkali  must  be  determined  and  different  crops  grown  to  learn 
the  effects  of  varying  quantities  of  salts  upon  them.     After  getting 
this  information  the  determination  of  the  alkali  of  new  lands  will 
give  a  very  good  idea  of  the  crops  to  grow.     Many  plants  are  most 
sensitive  to  alkali  when  young  and  some  special   precautions  must 
he  taken  in  starting  them.     As  a  general  rule  shallow  rooting  crops 
are  more  sensitive  than  the  deeper  rooting  ones,  such  as  alfalfa  and 
melilot.   whose   roots  extend    beyond   the   /one  of  greatest   concen- 
tration. 

2.  Retarding  Evaporation. — Alkali  salts  do  most  of  their  in- 
jury when  near  the  surface.     They  are  brought  there  by  the  upward 
.movement  and  evaporation  of  water,  and  anything  that  will  prevent 

this  will  retard  the  accumulation  of  salts  in  the  /one  of  greatest 
injury.  This  may  be  done  in  two  ways — by  mulching  and  shading. 
The  efficiency  of  a  layer  of  soil  in  fine  tilth  to  prevent,  evaporation 
has  already  been  discussed.  This  should  be  three  or  four  inches 


286 


SOIL  PHYSICS  AND  MANAGEMENT 


deep  to  be  most  effective  (Fig.  130).  This  mulch  if  maintained 
will  prevent  excessive  capillary  movement  until  the  crop  is  suffi- 
ciently large  to  shade  the  ground.  The  maintenance  of  the  mulch 
then  becomes  of  less  importance.  Alfalfa  during  three-fourths  of 
the  time  of  its  growth  furnishes  a  very  effective  shade.  Evaporation 
from  soil  of  orchards  is  prevented  very  materially  by  the  shading  of 
the  trees.  Artificial  mulches,  as  straw,  leaves,  sawdust,  and  manure, 
may  be  used,  but  are  too  expensive  for  large  areas  and  only  possible 
for  high-priced  crops  under  a  very  intensive  system  of  agriculture. 
3.  Deep  Plowing  and  Turning  Under  Alkali. — The  practice 
of  encouraging  evaporation  is  sometimes  resorted  to  for  bringing 
the  alkali  to  the  surface  and  then  turning  under  so  deeply  that  it 


Fia.   130. — An  orchard  well  cultivated  prevents  the  rise  of  alkali.      (U.  S.   Reclamation 

Service.) 

will  not  rise  to  the  surface  until  after  the  young  crop  has  passed 
through  its  most  sensitive  stage.  By  this  means  alfalfa  and  other 
crops  may  be  started.  When  the  crop  attains  such  size  that  it  shades 
the  soil  and  the  roots  take  up  the  water  from  beneath,  comparatively 
little  moisture  evaporates  from  the  surface  and  the  alkali  is  not 
carried  up  to  any  extent. 

4.  Neutralizing  Black  Alkali. — The  black  alkali  when  present 
in  amounts  of  one-tenth  of  a  per  cent  prevents  the  growing  of  most 
crops.  Sodium  sulfate  may  be  present  in  amounts  five  times  as 
great  before  it  becomes  injurious.  By  treating  the  black  alkali 
spots  with  gypsum  (land  plaster)  a  chemical  reaction  takes  place 
when  moisture  is  present,  producing  sodium  sulfate  and  calcium 
carbonate.  The  former  is  not  sufficiently  soluble  to  be  injurious, 


ALKALI  LANDS  AND  THEIR  RECLAMATION  287 

while  the  latter  is  very  beneficial  to  the  soil  in  its  puddled  condi- 
tion.    The  reaction  is  as  follows: 


CaS04  =  Xa2S04  +  CaC03. 

The  amount  to  be  applied  depends  upon  the  amount  of  alkali 
present.  Twice  as  much  gypsum  as  black  alkali  is  needed,  but  it  is 
best  to  apply  200  to  400  pounds  per  acre  annually.  Moisture  is 
necessary  for  the  reaction  to  take  place.  The  change  in  the  phy- 
sical condition  of  the  soil  is  as  important  as  the  chemical  effect.  The 
impervious  soil  begins  to  swell  up,  becomes  porous  and  soon  the  de- 
pressed spot  is  brought  to  the  general  level. 

5.  Removing  the  Salts  from  the  Soil.  —  The  removal  of  the 
salts  is  the  only  permanent  remedy  for  reclaiming  alkali  lands. 
This  is  accomplished  in  several  ways. 

(a)  By   tfcrapiny.  —  When    excessive   evaporation    has    brought 
large  quantities  of  alkali  to  the  surface  it  may  be  scraped  off  with 
two  or  three  inches  of  soil  and  thrown  into  drainage  systems  that 
will  carry  them  off  the  land.     Large  amounts  of  alkali  may  be  re- 
moved in  this  way,  but  this  applies  to  small  areas  only. 

(b)  Flooding.  —  The  alkali  may  be  leached  doirnirard  into  the 
soil  to  a  depth  of  three  or  four  feet  by  Hooding  so  that  the  crop  may 
be  temporarily  relieved  from  any  danger  of  injury.     Attempts  have 
been  made  to  wash  the  salts  off  the  land,  but  since  they  soak  into 
the  soil  as  soon  as  dissolved  this  is  impossible. 

(c)  By  Cropping.  —  This  method  is  to  produce  crops  that  take 
up  large  amounts  of  alkali  in  their  growth  which  will  be  removed 
with  the  crop.     The  Australian  salt  bush  when  mature  contains  20 
per  cent  of  ash  and  yields  as  much  as  five  tons  per  acre.      A  single 
crop  will  remove  approximately  a  ton  of  alkali. 

(d)  Underdrawn  ge.  —  Leaching  out    the   salts   through    under- 
drainage  is  the  most  practical  a'nd  permanent  remedy  that  has  been 
devised.     This,  of  course,  requires  a  thorough  drainage  system  as 
complete  as  for  draining  the  swamps  of  humid  regions.     After  the 
drainage  system  is  installed,  the  soil   must  be  flooded  to  leach  out 
a  large  per  cent  of  the  salts,  so  that  there  will  be  little  danger  from 
alkali  later.     Tin's  requires  a  large  amount  of  water,  as  the  flooding 
must  continue  for  several  months  (  Fi<r.  i:?1).     With  every  irriga- 
tion system  a  corresponding  underdrainasre  svstem  should  be   in- 
stalled to  carry  off  the  water  from  excessive  irrigation  and  seepage. 
which  is  largely  responsible  for  the  rise  of  alkali. 

To  give  an  idea  of   the  way   reclamation   is  accomplished  by 


288 


SOILS  PHYSICS  AND  MANAGEMENT 


ALKALI  LANDS  AND  THEIR  RECLAMATION  289 

leaching  let  us  consider  briefly  the  work  on  a  40-acre  tract  reclaimed 
near  Salt  Lake  City.  The  soil  was  badly  affected  by  alkali,  there 
being  from  2.5  to  5  per  cent  to  a  deptli  of  four  feet.  The  salts 
were  principally  sodium  chlorid  and  sodium  sulfate,  and  since  0.25 
per  cent  of  the  former  and  0.5  per  cent  of  the  latter  represent  the 
upper  limit  of  resistance  of  most  farm  crops  it  will  be  seen  that  the 
land  was  worthless. 

The  work  began  in  1902,  the  Bureau  of  Soils  and  Utah  Station 
cooperating.5  A  system  of  underdrainage  was  installed,  the  laterals 
being  three-inch  and  four-inch  tiles,  150  feet  apart  and  placed  four 
feet  deep.  The  soil  was  a  sandy  and  silty  loam  from  12  to  18 


- 


Fio.   132. — Wheat  on  rerlnimod  alkali  land  nonr  Fresno,  Cal.      Tlrolnimpd  by  one  year  of 
flooding  with  underdrainage.      (U.  S.  Dept.  Agr.) 

inches  deep;  the  underlying  material  varied  from  heavy  loam  to 
clay.  The  total  volume  of  water  used  in  flooding  was  17,8!)(!,K(>(i 
cubic  feet  or  10.2  feet  deep  over  the  40  acres.  The  total  salts  re- 
moved in  the  8,775,040  cubic  feet  of  drainage  water  was  1  0,(>3  \. 000 
pounds  of  5317  tons,  or  about  one  and  one-fourth  pounds  per  <  ubic 
foot  of  water.  The  amount  of  alkali  in  the  soil  at  the  beginning 
was  0051  tons.  About  HO  per  cent  was  removed. 

The  cost  of  installing  the  drainage  system  was  .$!(>. 50  per  acre. 

A  20-acre  tract  at  Fresno,  California,  was  reclaimed  in  a  similar 

way,  the  cost  of  installing  the  drainage  system  being  the  same  as 

for  the  Utah  area  (Fig.  132).     Tin's  land  bad  been  purchased  for 

$350   per  acre  and   was   abandoned    10   years   after   its   purchase. 

19 


290  SOIL  PHYSICS  AND  MANAGEMENT 

Flooding  was  begun  on  March  1,  1903,  and  in  November,  1903, 
alfalfa  was  seeded  on  three  acres,  which  was  cut  six  times  the  next 
year,  producing  a  total  of  25,000  pounds  of  alfalfa  hay. 

Other  tracts,  North  Yakima,  Washington,  Billings,  Montana, 
and  Tempe,  Arizona,  were  reclaimed.  The  cost  of  installing  the 
drainage  system  varied  from  $21  to  $35  per  acre. 

Hardpan. — Where  hardpan  occurs  in  the  subsoil  reclamation  is 
a  much  more  difficult  process.  This  layer  usually  varies  in  depth 
from  one  to  four  feet  or  even  more.  The  cementing  material  may 
be  calcium  carbonate,  iron  compounds  or  other  substances  and  may 
be  from  a  few  inches  to  several  feet  in  thickness.  In  some  instances 
the  action  of  the  water  is  to  disintegrate  the  hardpan,  and  where 
this  occurs  little  difficulty  is  caused  by  it.  Calcium  carbonate  some- 
times acts  in  this  way.  Usually  this  does  not  occur  and  it  becomes 
practically  impossible  to  leach  out  the  alkali  because  the  hardpan 
will  not  permit  the  water  to  pass  downward.  The  alkali  may  be 
leached  to  the  depth  of  the  hardpan,  but  much  of  it  remains  in  this 
stratum  and  soon  rises.  If  the  hardpan  is  due  to  black  alkali  it  is 
necessary  to  neutralize  this  with  gypsum  before  flooding. 

Most  soils,  especially  silt  loams,  clay  loams,  and  clays,  are 
injured  more  or  less  by  flooding.  The  granules  are  destroyed,  so 
that  when  the  water  is  removed  the  soil  bakes  or  is  partly  puddled, 
and  it  becomes  necessary  to  use  some  means  for  restoring  the  tilth. 
This  may  be  accomplished  by  turning  under  a  green  manure  crop 
or  by  an  application  of  farmyard  manure. 

Value  of  Alkali  Land. — Alkali  lands  include  some  of  the  most 
valuable  lands  in  the  West,  but  more  especially  those  that  are 
capable  of  being  irrigated.  They  are  worthless  as  they  are,  but 
after  the  alkali  is  removed  they  have  a  very  high  value.  Where 
water  may  be  had  in  abundance  the  cost  of  reclaiming  is  not  exces- 
sive. In  doing  this  reclamation  work  drainage  districts  should  be 
organized  similar  to  those  in  humid  regions  for  draining  swamp 
land.  The  expense  would  in  this  way  be  reduced  to  a  reasonable 
amount  per  acre. 

Alkali  Soils  of  Humid  Regions. — In  areas  where  the  rainfall 
would  seem  to  preclude  the  possibility  of  alkali,  soils  are  sometimes 
found  to  contain  considerable  amounts  of  soluble  material. 

Dorsey  e  speaks  of  the  patches  of  alkali  at  the  Maryland  Station, 
where  a  thin  layer  of  soil  showed  1.83  per  cent  of  water-soluble  salts, 
such  as  nitrates  of  calcium,  magnesium,  sodium,  and  potassium, 
together  with  some  chlorides  and  sul fates. 


ALKALI  LANDS  AND  THEIR  RECLAMATION 


291 


Small  spots  a  few  rods  in  diameter  occur  in  southern  Illinois  in 
which  the  soluble  salts  form  a  deposit  that  looks  like  a  heavy 
white  frost  or  light  snow.  Analysis  shows  this  to  be  sodium  sulfate. 
It  has  been  brought  to  the  surface  by  seepage  from  higher  land. 

In  the  glaciated  area  of  the  Middle  West  alkali  soils  occur  in 
many  low,  swampy  places,  usually  in  small  patches  of  a  few  square 
rods,  but  in  some  cases  extend  over  many  acres.  During  dry  spells 
whitish  incrustations  appear  on  the  surface  of  the  soil  that  disap- 
pear with  rains  (Fig.  133).  These  alkali  areas  almost  always  con- 


Fio.   133. — A  dwarfed  bushy  or  loafy  porn  plant  (jrowinjf  on  nlkali  soil  of  humid  nron. 
Sholls  arc  nearly  always  indications  of  alkali. 

tain  large  quantities  of  magnesium  carbonate,  and  when  this  com- 
pound amounts  to  more  than  one  per  cent  crops  such  as  corn  and 
oats  are  badly  affected.  The  corn  does  not  grow  well,  and  where 
strongly  impregnated  with  the  carbonate  is  bushy  and  the  blades 
turn  brown  or  reddish.  If  a  smaller  amount  is  present  the  blades 
are  striped  with  yellow.  Very  little  grain  is  produced.  Oats 
make  a  rank  growth,  but  almost  invariably  lodge. 

Drainage  is  the  ultimate  remedy,  but  the  process  is  slow  when 
only  the  natural  rainfall  is  depended  upon. 


292  SOIL  PHYSICS  AND  MANAGEMENT 

However,  for  immediately  correcting  the  effect  of  the  alkali 
applications  of  from  75  to  200  pounds  of  potassium  salts  may  be 
used  when  they  can  be  obtained  at  reasonable  prices  (Fig.  194). 
Coarse  stable  manure  is  as  efficient  as  potassium  salts,  and  even 
straw  or  green  manure  turned  under  has  a  very  beneficial  effect. 

QUESTIONS 

1.  What  conditions  give  rise  to  alkali  soils? 

2.  On  what  kind  of  lands  as  to  topography  is  alkali  most  abundant? 

3.  What  is  the  source  of  the  alkali  salts? 

4.  What  is  the  composition  of  black  alkali? 

5.  What  salts  constitute  the  white  alkali  ? 

6.  Note  effects  of  black  alkali  upon  the  soil  and  organic  matter. 

7.  How  many  pounds  of  alkali  in  the  surface  foot  of  soil  in  each  column 

in  the  table  of  page  282  ? 

8.  How  does  irrigation  cause  a  rise  of  alkali? 

9.  What  are  "alkali  marshes"? 

10.  What  is  the  first  effect  of  alkali  on  plants  ? 

11.  What  is  the  nature  of  the  effect  of  alkali  upon  trees? 

12.  Is  the  effect  of  alkali  the  same  on  all  plants? 

13.  What  effect  does  alkali  have  on  germination  ? 

14.  Why  are  shallow  rooted  crops  more  affected  by  alkali  ? 

15.  What  methods  are  adopted  for  preventing  evaporation? 

16.  What  means  are  taken  to   start  crops  whose  young  plants   are  very 

sensitive  to  alkali  ? 

17.  How  is  black  alkali  neutralized? 

18.  What  objections  to  removal  of  alkali  by  scraping? 

19.  Why  cannot  alkali  be  washed  off  of  land? 

20.  How  may  the  Australian  salt  bush  be  used  to  remove  alkali  ?     Does 

this  plant  have  any  value? 

21.  Describe  the  reclamation  of  the  Utah  tract. 

22.  What  percentage  of  the  water  applied  was  carried  off  by  drainage? 

23.  Why  is  a  hardpan  detrimental  in  removing  alkali  ? 

24.  What  is  the  effect  of  flooding  on  tilth?     How  may   the  condition  be 

corrected  ? 

25.  What  is  the  importance  of  reclamation  of  alkali  lands  from  an  economic 

standpoint? 

26.  Why  do  alkali  soils  occur  in  humid  regions?    How  does  the  alkali  differ 

from  that  of  arid  regions? 

27.  What  is  the  substance  that  does  the  injury? 

28.  How  is  corn  affected  by  magnesium  carbonate? 

29.  What  are  the  remedies  to  be  used? 

REFERENCES 

1  Hilgard,  E.  W.,  Soils,  1906,  pp.  442-43. 

'Hilgard,  E.  W.,  Report  of  California  Station,  1894-95. 

*  Op.  Cit.,  p.  449. 
4  Op.  Cit.,  p.  467. 

"Dorsey,  C.  W.,  Bulletin  35,  Bureau  of  Plant  Industry,  U.  S.  D.  A.,  Alkali 
Soils  of  the  United  States,  1906,  pp.  174-194. 

•  Op.  Cit.,  p.  157. 


CHAPTER  XXIII 

TEMPERATURE 

THE  vital  functions  of  plants  require  a  certain  temperature  for 
their  best  performance.  Plants  may  grow  at  other  temperatures,  but 
they  grow  most  vigorously  at  the  optimum  temperature,  which  for 
different  plants  varies  from  KO  to  100  degrees  F.  Below  this  growth 
diminishes  till  at  about  40  degrees  F.  it  ceases  for  most  plants.  At 
temperatures  higher  than  the  optimum  growth  is  less  vigorous  till  a 
point  is  reached  at  from  5)!)  to  115  degrees  F.,  where  it  practically 
ceases.  A  knowledge  of  the  functions  of  heat  in  relation  to  germi- 
nation, growth,  physical  phenomena,  and  bacterial  activity,  and  the 
means  of  its  control,  is  of  considerable  practical  importance  to  the 
agriculturist. 

The  Sources  of  Soil  Heat. —  1.  Direct  Radiation  from  the 
Sun. — The  sun  gives  off  both  light  and  heat  rays,  and  some  of  the 
latter,  striking  the  earth,  are  absorbed.  This  is  the  chief  source 
of  heat.  The  amount  received  from  the  sun  is  enormous.  Lang- 
ley  gives  it  as  equal  to  1,000,000  calories  per  hour  per  square 
meter  of  surface  from  a  vertical  sun  in  a  clear  sky.  If  all  of  this 
energy  were  absorbed  by  the  plowed  six  inches  of  soil  on  a  square 
foot  its  temperature  would  be  raised  by  24.5  degrees  in  an  hour. 
The  soil  is  always  radiating  heat,  consisting  of  waves  of  lower  pitch. 
These  are  easily  held  by  glass  or  water  vapor,  which  is  transparent 
to  waves  of  higher  pitch  or  refrangibility.  Hence  the  excessive  heat 
of  the  glass  house  and  the  oppressive  heat  when  the  air  is  laden 
with  moisture  in  the  summer. 

The  heat  received  by  any  part  of  the  earth's  surface  from  the 
sun  depends  upon  the -transparency  of  the  atmosphere  to  heat.  Dust 
particles  and  water  vapor  in  the  atmosphere  intercept  some,  while 
dry  air,  free  from  dust,  absorbs  very  little. 

Comparing  the  highest  temperature  reached  by  a  blackened 
thermometer  in  vacuo  at  Greenwich,  England,  near  sea  level,  and  at 
Davos,  Switzerland,  5100  feet  above  sea  level,  the  temperature  at 
the  latter  place  was  20.1  degrees  F.  higher  in  Xovember,  3f>.2  degrees 
in  December,  37.2  degrees  in  January,  and  24.2  degrees  in  Feb- 
ruary. The  ground  was  continuously  covered  with  snow  at  Davos. 
While  more  heat  is  received  from  the  sun  at  high  altitude  per  unit 

293 


294 


SOIL  PHYSICS  AND  MANAGEMENT 


area,  it  is  radiated  into  space  much  more  rapidly  because  of  the 
small  amount  of  vapor  in  the  air  to  hold  it. 

2.  Precipitation. — When  warm  rain  falls  upon  and  penetrates 
the  cold  soil  it  carries  with  it  large  amounts  of  heat.     This  may 
account  for  the  rapid  growth  of  plants  after  a  shower  in  spring. 
An  inch  of  rain  10  degrees  warmer  than  the  soil  would  raise  the 
temperature  of  the  surface  six  inches  of  soil  4.6  degrees  if  10  per 
cent  of  moisture  existed  in  the  soil  to  begin  with. 

3.  Chemical  changes  in  the  soil  result  in  the  production  of 
heat.     This  is  especially  true  of  all  chemical  changes  in  organic 
matter,   but  particularly  so  of  green  crops  and   fresh  farmyard 
manure.    The  results  of  some  experiments  at  the  Imperial  College, 
Tokio,  Japan,  with  different  amounts  of  manure  applied  and  thor- 
oughly mixed  with  the  soil,  are  given  for  five-day  intervals  in  the 
accompanying  table: 

Influence  of  Farmyard  Manure  on  Temperature  of  Soil.1    Degrees  Fahrenttrit 


Tons  per  acre  

None 

10 

20 

40 

80 

Temperature,  October  27-31  . 

60.5 

62.5 

63.8 

63.1 

65.1 

Excess  over  unmanured  

2.0 

3.3 

2.6 

4.6 

Temperature,  November  1-5  

58.5 

59.5 

60.2 

61.3 

62.2 

Excess  over  unmanured  

1.0 

1.7 

2.8 

3.7 

Temperature,  November  6-10 

57.2 

57.8 

58.4 

59.3 

60.4 

Excess  over  unmanured 

0.6 

1.2 

2.1 

3.2 

Temperature,  November  11-15  

54.7 

54.8 

55.3 

56.2 

56.8 

Excess  over  unmanured  

0.1 

0.6 

1.5 

2.1 

Average  excess  with  manure  in  first  twenty 
davs  .  . 

0.93 

1.70 

2.25 

3.40 

It  will  be  noted  that  the  heavier  the  application  the  greater  the 
increase  in  temperature. 

4.  Physical  Changes. — When  a  soil  absorbs  water  its  tempera- 
ture is  increased.  This  is  true  for  both  water  vapor  and  liquid 
water,  the  former  producing  the  highest  temperature  because  of  the 

Increase  in  Temperature  by  Absorption  of  Water  Vapor  at  86  Degrees  F. 
(SO  Degrees  C.)2 

Quartz  sand 1.58°  F.  (  0.88°  C.) 

Calcium  carbonate  (precipitated) 2.64°  F.  (  1.47°  C.) 

Kaolin 4.73°  F.  (  2.63°>C.) 

Hydrated  ferric  oxide 16.74°  F.  (  9.30°  C.) 

Peat..  ...  22.05°  F.  (12.25°  C.) 


TEMPERATURE  295 

latent  heat  given  off  during  condensation.    The  greater  the  hygro- 
scopic capacity  of  the  soil  the  higher  is  the  temperature  produced. 

From  the  preceding  table  on  page  294  it  will  he  seen  that  peat 
and  ferric  oxide  gave  the  highest  temperature,  while  quartz  sand, 
with  its  low  hygroscopic  capacity,  gave  the  least  increase.  In 
the  next  table  the  increases  are  not  so  large. 

Increase  of  Temperature  by  the  Application  of  Liquid  Water  at  50  Degrees  F. 

(10  Degrees  C.)2 

Quartz  sand 18°  F.  (  .10°  C.) 

Calcium  carbonate  (precipitated) 50°  F.  (  .28°  C.) 

Kaolin 1.49°  F.  (  .83°  C.) 

Hydrated  ferric  oxide 11 .88°  F.  (0.60°  C.) 

Loss  of  Heat. — While  the  soil  is  receiving  heat  through  these 
various  sources  it  is  losing  it  in  several  different  ways. 

1.  By  Radiation. — The  amount  of  heat  radiated  from  soils  is 
not  directly  affected  by  their  color.  The  statement  is  made  in 
physics  that  good  absorbers  are  good  radiators.  This  is  also  true 
that  the  heat  lost  by  radiation  and  convection  by  one  body  to  another 
surrounding  it  is  proportional  to  the  temperature  difference  between 
the  two.  Dark  soils  are  good  absorbers  of  the  sun's  heat,  but  they 
have  no  tendency  to  lose  it  more  rapidly  because  of  their  color,  but 
because  they  are  warmer  than  poor  absorbers  or  light  colored  soils, 
and  at  night  they  all  tend  to  cool  to  the  temperature  of  the  sur- 
rounding atmosphere.  Black  soils  having  absorbed  more  heat  will 
have  more  to  radiate,  but  there  is  no  tendency  for  dark  soils  to 
become  lower  in  temperature  at  night  than  light-colored  ones  under 
the  same  conditions. 

In  order  to  determine  the  effect  of  color  on  radiation  Bouyoucos 
colored  white  sand  and  determined  the  radiation  ratio  as  given  in 
the  following  table: 

The  limitation  Ratio  of  Different  Colored  Sandu 


Colored  Himcl 

Radiation  ratio 

White  .  . 

1  .(XiO 

Black  

.061 

Blue  

.()4.r> 

(Jreen                                                                          

.040 

Red  

.050 

Yellow.  . 

.048 

296  SOIL  PHYSICS  AND  MANAGEMENT 

The  results  seem  to  indicate  that  radiation  is  slightly  better  from 
white  sand,  but  the  differences  are  so  small  that  they  come  within 
the  experimental  error,  and  so  the  conclusion  is  reached  by  the 
experimenter  that  color  does  not  affect  radiation.  A  large  amount 
of  the  heat  radiated  from  the  soil  is  brought  to  the  surface  by  con- 
duction. It  is  absorbed  during  the  day  and  is  conducted  downward 
to  a  depth  of  from  one  to  twelve  inches.  As  the  temperature  of  the 
air  becomes  lower  at  night  the  heat  in  part  is  conducted  back  to  the 
surface  and  is  radiated  into  the  air.  From  February  to  August 
mere  heat  is  received  by  the  soil  than  is  radiated  from  it,  but  during 
the  rest  of  the  year  radiation  is  greater  than  absorption,  and  as  a 
result  the  temperature  of  the  soil  is  becoming  lower.  (See  the 
table,  page  307.) 

2.  By  Conduction  Downward  Into  the  Soil. — The  process  of 
conduction  is  a  very  slow  one,  so  slow  that  the  soil  at  a  depth  of 
36  inches  has  an  average  annual  range  of  only  28.7  degrees  F.  for  a 
ten-year  average,  while  at  a  depth  of  one  inch  the  average  range  was 
45.8  degrees.    Some  of  the  heat  is  conducted  to  such  a  depth  that  it 
cannot  influence  the  growth  of  plants  in  any  way  and  may  be  con- 
sidered lost. 

3.  By  Evaporation  of  Water. — When  water  is  evaporated  large 
amounts  of  heat  are  carried  away  as  latent  heat  in  the  vapor. 

4.  By  Convection  Currents  of  Air. — The  heated  soil  warms 
the  adjacent  air,  causing  it  to  expand  and  rise.     These  currents  of 
warm  air  are  constantly  carrying  large  amounts  of  heat  upward. 
The  effect  of  this  in  comparison  to  radiation  may  be  seen  by  placing 
thermometers  at  equal  distances  above  and  on  the  side  of  a  heated 
object. 

Soil  Temperature  for  Vital  Functions  of  Plants. — 1.  Tem- 
perature for  Germination. — The  temperature  at  which'  ger- 
mination takes  place  varies  with  different  classes  of  plants. 
Slow  germination  in  a  cold  soil  brings  about  favorable  con- 
ditions for  the  action  of  fungi  and  bacteria  upon  the  seed  which  may 
cause  decay.  Some  of  our  cultivated  crops,  as  corn  and  beans,  are 
especially  susceptible  to  injury  in  this  way.  This  may  bring  about 
a  low  percentage  of  germination  and  a  poor  stand  results.  Uloth  * 
found  that  certain  seeds,  one  of  which  was  wheat,  would  germinate 
in  a  dark  cellar  on  a  cake  of  ice,  the  rootlets  descending  into  the  ice 
to  a  slight  depth  by  melting  cylindrical  cavities.  The  rootlets  of 
Norway  maple  descended  into  the  ice  to  a  depth  of  7.5  centimeters. 
The  next  table  gives  the  minimum,  optimum,  and  maximum  tem- 
perature at  which  germination  takes  place. 


TEMPERATURE 


297 


Minimum,  Optimum,  and  Maximum  Temperatures  far  Germination  oj  Various 
Seeds  as  Determined  by  Different  Investigators  (Degrees  Fahrenheit) 


Investigator 

Minimum 

Optimum 

Maximum 

Sachs 

Van 

Tieg- 
ham 

Haber- 
landt 

Sachs 

Van 
Tieg- 
ham 

Haber- 
landt 

Sachs 

Van 
Tieg- 
ham 

Haber- 
landt 

Wheat    

41 
41 
44.5 

48 

41 
41 
44 
49 

42 

32-40 
32-40 
32-40 
40-51 
32-40 
32-40 
32-40 
60-65 
51-60 
32-40 

84 
84 
84 
93 

84 
83 
80 
93 
70 
89 
81 
99 

77-88 
77-88 
77-88 
88-100 
77-100 
77-88 
61-88 
88-100 
100 
77 

104 
104 
102 
115 

.    .    . 

99 
100 

115 
82 
108 
99 

100 
100 
100 
111-122 
100-111 
88-100 
88-100 
111-122 
111-122 
88-100 

Barley  

Peas  
Corn  (maize^ 
Red  clover  .  . 
Turnip  

Mustard 

32 

Melon  

Pumpkin  .  .  . 
Oats  

By  consulting  the  following  table  it  will  be  seen  that  we 
long  ago  adapted  our  agricultural  practices  to  conform  in  a  measure 
to  the  temperature  requirements  of  plants  for  germination.  The 
temperatures  for  growth  are  very  similar  to  those  for  germination. 

Time  Requited  fen  Appearance  of  Radicle  at  Different  Temperatures  5 


Temperatures  

40°  F. 

51°  F. 

60°  F. 

65°  F. 

Rve  

4 

2.5 

1 

1 

Wheat  and  barley  

6 

3 

2 

1.75 

Oats  

7 

3.75 

2.75 

2 

Vetches  

6 

5 

•» 

o 

Alfalfa  

6 

3.75 

2.75 

2 

Red  clover  

7.5 

3 

1.75 

1 

Beans 

7 

6.5 

4.75 

4.25 

Mustard  

2 

1.5 

1 

0.75 

Peas  

5 

3 

1.75 

1.75 

Rape  

6 

2 

1 

1 

Turnip. 

8 

4 

•) 

1.75 

Sugar  IxH't  

22 

9 

3.75 

3.75 

Flax  

8 

4.5 

2 

2 

Corn  (maize)  

11.25 

3.25 

3 

Pumpkin  

10.75 

4 

It  will  be  seen  from  the  preceding  table  that  the  time  for  germi- 
nation is  controlled  largely  by  the  temperature  and  emphasizes  the 
necessity  of  not  seeding  until  the  temperature  is  high  enough. 

2.  Temperature  for  Growth.- — With  most  plants,  and  espe- 
cially with  our  cultivated  ones,  growth  does  not  begin  until  a  tern- 


298 


SOIL  PHYSICS  AND  MANAGEMENT 


perature  of  40  to  50  degrees  F.,  the  zero  point  of  growth,  is  reached 
by  the  soil.  Growth  is  most  vigorous  at  from  80  to  90  degrees  F. 
This  means  that  the  temperature  must  reach  that  point  during  the 
day,  even  if  it  does  fall  below  this  during  the  night.  The  amount 
of  growth  depends  upon  the  proportion  of  the  day  that  is  above  the 
zero  point  of  growth  or  the  heat  hours.  It  will  be  seen-  from  the 
following  table  that  corn  requires  a  medium  high  temperature  before 
growth  begins,  while  melons  require  a  still  higher  one. 

Temperature  of  Soil  for  Growth  6 


Crops 

Minimum 

Optimum 

Maximum 

Mustard  

32°  F. 

81     °F. 

99     °F. 

Barley  

41°  F. 

83.6°  F. 

99.8°  F. 

Wheat 

41°  F 

836°  F 

108  5°  F 

Maize  

49°  F. 

93.6°  F. 

115    °F. 

Kidney  bean  

49°  F. 

92.6°  F. 

115    °F. 

Melon  

65°  F. 

91.4°  F. 

Ill    °  F. 

3.  Temperatures  Favorable  for  Osmosis  and  Diffusion.— 
Osmosis  is  a  process  upon  which  germination  of  seeds  and  the 
growth  of  plants  depend.    The  seed  coat  is  the  osmotic  membrane, 
and  the  rapidity  with  which  water  passes  through  this  depends  upon 
the  temperature.    Osmotic  pressure  is  the  power  that  sends  the  soil 
moisture  into  the  roots  of  plants.    At  low  temperatures  plants  may 
wilt,  and  Sachs  found  that  at  55  degrees  F.  pumpkin  and  tobacco 
plants  did  not  receive  sufficient  moisture  to  compensate  for  even-  slow 
transpiration. 

Diffusion  of  substances  in  solution  is  influenced  by  tempera- 
ture in  the  same  way,  being  much  more  rapid  at  high  than  low 
temperatures. 

4.  Temperatures    for    Nitrification.  —  Our    ordinary    crops 
depend  to  a  large  extent  upon  the  activity  of  bacteria  in  the  soil, 
which  by  means  of  the  process  of  nitrification  use  the  nitrogen  in 
the  organic  matter  to  produce  soluble  nitrates.    The  soil  bacteria  do 
not  work  to  any  large  extent  if  the  temperature  of  the  soil  is  below 
41  degrees  F.,  nor  above  130  degrees  F.     They  are  most  active 
at  temperatures  between  60  and  85  degrees  F. 

Conditions  Affecting  Soil  Temperature. — 1.  Specific  Heat. 
—It  is  a  very  interesting  as  well  as  an  important  fact  that  the  same 
amount  of  heat  applied  to  different  substances  raises  the  temperature 


TEMPERATURE 


299 


unequally.  Of  all  substances,  solid  or  liquid,  water  requires  the 
greatest  amount  of  heat  to  change  its  temperature  one  degree.  The 
quantity  of  heat  required  to  change  the  temperature  of  a  unit  mass 
of  any  substance  one  degree  is  the  specific  heat  of  the  substance. 
Water  is  taken  as  unity. 


Specific  Heats  of  Some  Common  Substances' 


Aluminum 

0.219 

Lead 

.   0.305 

Brass  

0.09 

Quartz  

0.174 

Copper  

.  .    .  .     0.0936 

Silver     

0.0559 

Glass 

0.117 

Tin          

.    .        .       0.0552 

Granite  

0.19  to  0.20 

Zinc  

0.0935 

Iron  

0.119 

Mercury  

0.0333 

This  means  that  one  pound  of  iron  requires  0.119  as  much  heat 
to  change  its  temperature  one  degree  as  is  required  by  a  pound  of 
water,  or  that  the  heat  necessary  to  effect  a  change  of  one  degree  in 
a  pound  of  water  would  raise  8.4  pounds  of  iron  one  degree,  or  one 
pound  8.4  degrees. 

Dry  soils  generally  possess  a  low  specific  heat,  varying  from  0.15 
to  0.3,  with  an  average  of  0.215,  or,  in  other  words,  it  requires  from 
one-seventh  to  one-third  as  much  heat  to  raise  the  temperature  of  dry 
soil  one  degree  as  of  water. 

Specific  Heat  of  Soil  Constituents 


ng 

Equal 
weights 

Equal 
volumes 

Equal 
weights 

Equal 
volumes 

Sand.. 

0.189 

0.499 

0.1929 

0.509 

Clay  

0.233 

0.568 

0  206 

0.569 

Loam  .    . 

0.214 

0215 

0.551 

Peat  

0.477 

0.587 

0.253 

0.440 

Ferric  oxide  

0.163 

0.831 

Calcium  carbonate  

0.206 

0  561 

Gravel  

0.2045 

0.554 

The  figures  for  peat  vary  a  great  deal,  localise  in  some  cases  no 
allowance  was  made  for  the  heat  of  wetting.  The  specific  heat  of 
equal  volumes  may  be  obtained  by  multiplying  the  specific  heat  of 
equal  weight  by  the  specific  gravity. 


300 


SOIL  PHYSICS  AND  MANAGEMENT 


Patten  has  made  determinations  of  the  specific  heat  of  soil  types 
of  various  classes  as  given  in  the  following  table : 

Specific   Heat   of  Soils    (Equal   Weights)  • 

Norfolk  sand  0.1848 

Hudson   River   sand 0.1769 

Fine  sand   (soil  separate) 0.1799 

Fine  quartz  flour 0.1900 

Coarse  sand   (quartz) 0.1900 

Podunk   fine  sandy   loam 0.1828 

Leonardtown  silt  loam 0.1944 

Hageratown  loam   0.1914 

Galveston  clay   0.2097 

Muck  soil,  25  per  cent   of  organic  matter 0.1 566 


Humus  has  the  highest  and  sand  the  lowest  specific  heat  of  soil 
constituents.  Wet  soils  require  much  more  heat  to  raise  their  tem- 
perature than  dry  ones.  In  case  of  a  dry  silt  loam  whose  specific 
heat  is  0.23  if  20  per  cent  of  moisture  is  added,  its  specific  heat  will 
be  raised  to  0.36.  One  hundred  pounds  of  dry  soil  would  require  the 
application  of  23  heat  units  to  raise  its  temperature  one  degree, 
while  the  same  weight  of  the  wet  soil  would  require  36  heat  units. 
The  latter  would  warm  up  much  more  slowly  than  the  former.  The 
effect  of  varying  amounts  of  moisture  on  the  specific  heat  is  here 
shown : 

Effect  oj  Moisture  on  Specific  Heat,  Podunk  Fine  Sandy  Loam  10 


Moisture  content, 

Moisture  content, 

per  cent  of  dry 
weight 

Specific  heat 

per  cent  of  dry 
weight 

Specific  heat 

0.268 

.1850 

6.60 

.2334 

1.33 

.1935 

10.08 

.2575 

2.14 

.2000 

20.25 

.3204 

2.83 

.2053 

26.93 

.3562 

2.  Evaporation  of  Water. — The  temperature  of  soils  is  lowered 
by  the  evaporation  of  water  from  them.  In  the  change  from  a  solid 
to  a  liquid  or  from  a  liquid  to  a  vapor  heat  is  required  to  effect  the 
change.  When  the  opposite  change  takes  place  heat  is  liberated. 
When  ice  melts  80  calories  (centimeter-gram  system),  or  144  heat 
units  (English  system),  are  used  in  producing  the  changes  in  a  unit 
weight.  When  water  passes  into  vapor,  537  calories  or  966.6  heat 
units  are  required,  and  when  condensation  takes  place  this  heat  is 


TEMPERATURE 


301 


liberated.  When  water  evaporates  from  a  soil,  the  larger  part  of 
the  heat  used  in  the  process  is  taken  from  the  soil.  This  has  a 
tendency  to  lower  the  temperature,  and  hence  wet  soils  do  not  warm 
up  rapidly  in  the  spring  and  are  spoken  of  as  "  late  "  soils.  They 
become  warm  only  when  the  greater  part  of.  the  water  has  evaporated 
or  when  properly  drained. 

If  one-half  pound  of  water  is  evaporated  daily  from  a  square 
foot  of  soil,  4H.'J. 3  heat  units  or  121,790  calories  are  required,  the 
larger  part  of  which  would  be  taken  from  the  soil.  If  all  of  the  heat 
necessary  for  this  were  taken  from  a  cubic  foot  of  loam  soil  having 
an  apparent  specific  gravity  of  1.25  and  containing  20  per  cent  of 
moisture  it  would  lower  the  temperature  15.5  degrees  F. 

Clays,  peats,  and  undrained  soils  are  cold  and  late  partly  because 
of  this  evaporation. 

Anything  that  diminishes  evaporation  aid?  in  increasing  the 
temperature  of  soils.  Mulches,  windbreaks,  and  drainage  decrease 
evaporation,  and  hence  increase  temperature.  The  strong  winds  of 
spring  increase  evaporation,  hence  tend  to  keep  the  soil  cooler  until 
it  becomes  fairly  dry,  when  it  warms  up  rapidly. 

The  effect  of  the  wind  upon  evaporation  has  been  well  shown 
by  King,  who  determined  the  evaporation  at  20,  150,  and  300  feet 
to  the  leeward  of  a  hedgerow.  The  amount  was  24  and  33  per  cent 
greater  for  150  and  300  feet  respectively  than  at  20  feet.  When 
the  air  came  across  a  field  of  standing  clover  780  feet  wide  the 
evaporation  was  30.1  per  cent  greater  at  150  feet,  and  40  per  cent 
greater  at  300  feet  than  at  20  feet  from  the  field. 

3.  Drainage. — The  effect  of  drainage  on  temperature  at  differ- 
ent depths  is  shown  in  the  table.  The  soils  are  the  same.  Drainage 

The  Effect  of  Drainage  on  Temperature  n 


Time 

Thermometer 
1  inch  below 
surface 

Thermometer 
2  inches  below 
surface 

Thermometer 
4  inches  below 
surface 

Drained 

I"  nd  rained 

Drained 

1  'ml  rained 

Drained 

I'ndrained 

6  A.M  
Maximum  

6  P.M  

48.0°  F. 
82.5°  F. 
71.0°  F. 

49.0°  F. 
70.0°  F. 
63.0°  F. 

48.0°  F. 
S0.0°  F. 
7:5.0°  F. 

49.0°  F. 
09.0°  F. 
05.0°  F. 

49.5°  F. 
7f).0°  F. 
74.5°  F. 

49.0° 
(>S.4° 
67.5° 

F. 

F. 
F. 

removes  the  gravitational  or  free  water,  thus  lowering  the  specific 
heat  so  that  the  same  amount  of  heat  applied  will  raise  the  tempera- 
ture more  than  if  the  soil  contained  much  moisture. 


302 


SOIL  PHYSICS  AND  MANAGEMENT 


It  is  very  interesting  to  note  the  effect  of  drainage  in  the  above 
experiment  upon  the  germination  of  seeds  and  early  growth  of 
plants  in  the  drained  and  undrained  soil  (Fig.  95). 

4.  Presence  of  Water. — Aside  from  the  lowering  of  tempera- 
ture by  evaporation  of  water  from  soils,  the  presence  of  water  keeps 
the  temperature  down  because  of  the  slowness  with  which  it  changes 
or  because  of  its  high  specific  heat.     This  is  partly  the  cause  of 
peats,  clays,  and  undrained  land  being  cold  and  late.    If  a  cubic  foot 
of  dry  soil  having  a  specific  heat  of  0.2,  weighing  100  pounds,  should 
have  100  heat  units  applied  to  it,  its  temperature  would  be  increased 
five  degrees  Fahrenheit.    If  a  cubic  foot  should  contain  20  pounds 
of  water,  its  temperature  would  be  increased  two  and   one-half 
degrees,  or  the  specific  heat  of  the  soil  would  be  doubled.     Sand 
soils  are  "  early  "  because  of  the  small  amount  of  moisture  which 
they  contain  and  their  low  specific  heat. 

5.  Absorption  and  Radiation  of  Heat.  —  The  absorption  of 
heat  by  soils  and  consequently  their  temperature  depends  largely 
upon  their  color.    The  dark  colors  absorb  more  heat  than  light  ones. 
Black,  blue,  brown,  and  red  absorb  heat  in  the  order  given,  while 
green,  yellow,  gray,  and  white  absorb  less,  white  being  the  slowest 
absorber  of  all.    Bouyoucos  colored  white  sand  with  dyes  and  deter- 
mined the  comparative  absorbing  power  as  measured  by  the  tempera- 
ture obtained.    This  table  gives  the  results : 

Effect  of  Color  on  Temperature  of  Sands  M 


Color  of  sand 

July  27-28 

August  5-6 

Maximum 

2   P.M. 

Minimum 

4   A.M. 

Maximum 
2:30  P.M. 

Minimum 
4:30  A.M. 

Black.. 

40.9   °  C. 

40.0  °  C. 
38.55°  C. 
37.10°  C. 
35.8  °  C. 
34.6  °  C. 

16.7  °  C. 
16.65°  C. 
16.65°  C. 
16.60°  C. 
16.60°  C. 
16.44°  C. 

37.6   °  C. 

36.7  °  C. 
35.9  °C. 
34.7  °C. 
32.65°  C. 
31.7  °C. 

12.45°  C. 

12.4  °  C. 
12.4  °  C. 
12.3  °C. 
12.25°  C. 
12.2  °  C. 

Blue  

Red  

Green  

Yellow  

White  

A  very  interesting  demonstration  is  to  fill  a  tray  three  by  six 
feet  with  soil,  plant  an  equal  number  of  seeds  in  each  half  of  the 
tray,  and  cover  one-half  with  very  dark  soil  and  the  other  half  with 
white  soil  and  place  in  the  sunshine  (Fig.  134).  For  best  results 
this  should  be  carried  on  in  spring  or  fall.  Plants  come  up  from  24 


TEMPERATURE 


303 


to  72  hours  sooner  in  the  part  of  the  tray  covered  with  dark  soil. 
The  table  following  gives  the  temperature  in  the  two  parts  of 
the  tray : 

Effect  of  Color  on  Soil  Temperature  " 


Time 

Thermometer  bulb 
1  inch  below 
surface 

Thermometer  bulb 
2  inches  below 
surface 

Thermometer  bulb 
4  inches  below 
surface 

Light 

Dark 

Light 

Dark 

Light 

Dark 

6  A.M  
Maximum  .... 

48.8°  F. 
71.5°  F. 
71.5°  F. 

50.0°  F. 

82    °F. 
66.5°  F. 

47.5°  F. 

70.8°  F. 
74  5°  F. 

49.0°  F. 

78.5C  F. 
70    °F. 

48.5°  F. 

78.4°  F. 
77    °F. 

50.5°  F. 

71.3°  F. 
71    °F. 

G  P.M..  .  . 

Increase  

10.5°  F. 

8.8°  F.                        7.1°  F. 

Flo.    134. — Difference  in  growth  on  light  and  dark  colored  soils.     A.  corn ,  H.  wheat ;  C,  water- 
melon. 

The  time  and  the  number  of  plants  mining  through  the  soil 
are  governed  to  some  extent  by  the  color  of  the  soil,  as  is  shown  in 
the  following  table. 


304 


SOIL  PHYSICS  AND  MANAGEMENT 


Time  Required  and  the  \'umhcr  of  Plants  that  Came  Up  in  the  Soils  of  Different 
Colors.     One  hundred  Seeds  Were  Planted  in  Each  ll 


Days  after  pluming 

Wheat 

Oats 

Corn 

Melons 

Light 

Dark 

Light 

Dark 

Light 

Dark 

Light 

Dark 

7  

4 

75 
86 
86 
86 
86 
86 

27 
70 
75 
75 
75 

6 

80 
100 
100 
100 
100 
100 

i 

66 

72 
72 

6 
84 

95 
95 
95 

4 
32 

57 

21 
60 
85 
86 

8  

8 
29 
51 
58 
62 
65 

9  

10  

11  

12  

13  

With  black  the  absorption  is  almost  complete.  The  soils  of  what- 
ever color  tend  to  cool  to  the  temperature  of  the  surrounding 
atmosphere  during  the  night  or  in  cloudy  weather.  The  table  on 
page  302  shows  that  the  lowest  temperatures  of  the  dark-colored 
sands  were  not  as  low  as  the  light-colored  ones.  Color  has  little 
influence  in  very  wet  soils  since  evaporation  is  a  greater  factor  in 
lowering  temperature  than  color  is  in  raising  it. 

6.  Latitude  or  Angle  of  the  Sun's  Rays. — All  flat  areas  of 
the  earth's  surface  have  the  same  number  of  hours  of  possible  sun- 
shine annually  without  regard  to  location  on  the  earth.  The  effect 


Vertical 


Fia.   135. — Showing  the  comparative  areas  covered  by  the  sun's  rays  when  vertical,  30,  60, 
and  80  degrees  from  the  vertical.     Compare  AB,  AC,  AD,  and  AE. 

of  the  rays  in  warming  the  soil  depends  upon  the  angle  at  which 
they  strike  (Fig.  135).  If  a  sunbeam  striking  the  earth's  surface 
perpendicularly  covers  an  area  of  1,  when  this  same  beam  strikes 
at  an  angle  of  30  degrees  from  the  vertical,  it  will  cover  an  area  of 
1.175;  at  60  degrees  it  will  cover  an  area  of  2,  and  at  RO  degrees 
an  area  of  f>.  The  heat  will  be  spread  over  a  larger  area  the  greater 
the  distance  from  the  vertical,  and  the  effect  on  temperature  would 
be  inversely  as  the  angle.  The  atmosphere  absorbs  some  heat.  The 


TEMPERATURE 


305 


vertical  rays  pass  through  a  thinner  stratum  of  air  than  the  other, 
and  more  heat  will  reach  the  surface  from  a  vertical  sun.  The 
effect  of  greater  inclination  is  compensated  for  in  summer  to  some 
extent  by  the  longer  sunshine  period  in  twenty-four  hours  for  high 
latitudes. 

7.  Slope. — The  slope  of  land  has  somewhat  the  same  effect  as 
latitude  on  the  concentration  and  distribution  of  heat.  The  effect 
is  to  cause  the  rays  from  the  sun  to  strike  the  south  slope  at  a  less 
and  the  north  at  a  greater  angle  from  the  perpendicular  (Fig.  13(5). 
With  the  sun  45  degrees  above  the  horizon  and  the  hill  having  the 
two  slopes  of  20  degrees  of  equal  length,  the  south  one  would  receive 
twice  as  much  heat  from  the  sun  as  the  north  one. 

Wollny  found  that  the  average  temperature  of  the  south  slope  of 
a  15-degree  hill  was  1.5  degrees  F.  higher  than  the  north  slope. 


Fia.  13(>. — Effect  of  slope  on  the  area  covered  by  the  sun's  rays.  Angle  of  sun's  rays 
30  degrees  from  vertical.  KK  i.s  KM)  per  cent  greater  than  !)!•',.  BC  is  40  per  cent  greater 
than  AB. 

King  found  that  on  July  31  a  south  slope  of  IS  degrees  had  a  tem- 
perature 3.1  degrees  F.  higher  than  the  level  at  a  depth  of  one  foot  ; 
2.7  degrees  at  two  feet  and  'J.S  degrees  at  three  feet.  For  early 
crops  a  south  slope  is  desirable.  Plants  that  are  liable  to  injury 
from  spring  frosts  should  be  placed  on  north  slopes  so  that  growth 
will  be  retarded  as  much  as  possible. 
20 


306 


SOIL  PHYSICS  AND  MANAGEMENT 


8.  Conductivity  of  Soil  Material  and  Soils. — Wet  soils  are 
better  conductors  of  heat  than  dry  ones  and  compact  ones  better 
than  loose  ones.  These  differences  are  due  to  the  fact  that  air  is  a 
very  poor  conductor,  even  poorer  than  water.  Soils  should  not  con- 
duct heat  downward  very  rapidly  in  spring,  but  should  cause  concen- 
tration of  heat  in  the  surface  two  to  four  inches  to  hasten  germina- 
tion and  aid  the  growth  of  the 'young  plant.  Of  all  soil  materials 
quartz  shows  the  highest  rate  of  conductivity,  while  dry  powdered 
chalk  shows  the  lowest. 

In  the  following  table  it  will  be  well  to  note  the  difference 
between  loose  and  compast,  wet  and  dry,  and  fine  and  coarse. 

Relative  Conductivity  of  Soil  Material 13 


Soil  material 


D 

ry 

Wet 

Loose 

Compact 

100.0 
90.7 
90.7 
85.2 
112.1 
115.6 
100.0 
103.6 

10(5.7 
90.7 
96.4 
92.6 

201.7 
94.3 
155.6 
153.2 

105.3 
100.0 

moist 
174 

i89.6 

Quartz  powder 

Peat 

Kaolin 

Chalk.. 

Clay  with  limestone  stones 

Clay  with  quartz  stones 

Quartz  sand,  fine 

Quartz  sand,  medium 

Quartz  sand,  coarse 

Quartz  sand 

The  next  table  shows  the  length  of  time  required  after  the  air 
temperature  had  begun  to  rise  for  the  heat  to  penetrate  the  soil  to 
the  depths  given  in  the  table.  The  conductivity  of  soils  does  not 
play  a  great  part  in  practical  agriculture  except  early  in  the  spring 
when  the  greater  conductivity  of  sand  soils  permits  them  to  warm 
up  earlier  and  to  a  greater  depth,  thus  giving  the  crops  grown  upon 
them  the  advantage  of  several  hours  of  warmer  soils  each  day. 

Relative  Time  for  Heat  to  Penetrate  the  Soil  Under  Field  Conditions  14 


Date 

Depth 

Gravel 

Sand 

Loam 

Clay 

Peat 

inches 

hrs.     min. 

hrs.     min. 

hrs.     min. 

hra.     min. 

hrs.     min. 

July  27  

I         6 

4 

4 

6        30 

6 

9 

i       12 

7 

7 

9       30 

9       30 

August  5  

)       6 

4 

4 

6 

5       30 

8       30 

12 

7 

7 

10 

9       30 

August  26  

6 
12 

4       30 

7 

4       30 

7 

7 
10       30 

6 
10 

9 

August  27  

6 
12 

4 

6 

4 
6 

6 
10       30 

5       30 
10       30 

9 

September  

6 
12 

5 
5        30 

4 

5        30 

6       30 

9 

6 

9 

9       30 

TEMPERATURE 


307 


The  following  table  gives  the  average  soil  temperature  at  varying 
depths  for  ten  years : 

Average  Soil  Temperature,   1905-19 J 4     10-Year  Average  in  Rlucgrass  Sod11 


Depth  —  Inches 

Jan. 

Feb. 

30.9 
30.6 
31.5 
32.1 
32.7 
37.2 
38.8 

Mar. 

Apr. 

May 

June 

July 

Aug.  Sept. 

ot. 

Nov. 

Dec. 

1  

31.3 
31.5 
32.5 
33.2 
34.4 
39.4 
41.4 

40.0 
39.6 
38.9 
3S.3 
38.0 
3S.O 
40.2 

50.  U 
50.7 
49.6 
49.2 
48.7 
47.2 
46.1 

62.8 
62.2 
60.4 
59.8 
58.8 
55.3 
53.1 

72.7  76.7 
72.0i  75.8 
69.8  74.2 
68.5  73.5 
68.2!  72.8 
62.7!  68.3 
60.5  65.7 

76.4!  68.6 
75.8!  68.2 
74.0  68.2 
73.:*  67.9 
72.9!  67.6 
69.5i  66.7 
67.5|  65.9 

55.1 

.54.8 
54.9 
55.8 
5(5.9 
59.5 
60.4 

42.4 

42.8 
43.4 
44.3 
45.4 
49.9 
52.1 

35.6 
34.9 
35.3 
36.2 
37.8 
43.5 
45.8 

3  
6  

9  
12.    .    . 

24  
36  

It  will  be  noted  that  the  highest  average  temperature  to  a 
depth  of  nine  inches  is  readied  in  'July,  wbile  for  greater  depths  the 
highest  is  reached  in  August.  This  is  due  to  the  slow  conductivity 
of  the  soil. 

!>.  Tillage. — In  general,  tillage  has  two  effects  upon  soils  as 
regards  temperature.  It  increases  evaporation  at  first,  but  when  the 
surface  becomes  dry  this  layer  acts  as  a  mulch,  preventing  the  moist- 
ure from  coming  to  the  surface  when  the  heat  is  used  in  evaporating 
it.  Tillage  loosens  the  soil,  making  it  a  poor  conductor  of  heat. 
This  concentrates  the  heat  in  the  surface  two  or  three  inches  of 
soil,  and  gives  better  conditions  for  germination  early  in  the  spring. 
Later  in  the  season,  when  the  untilled  soil  has  become  somewhat 
dry,  the  conditions  are  reversed,  and  the  tilled  soil  is  cooler  than  the 
untilled. 

QUESTIONS 

1.  Why  is  a  knowledge  of  the  functions  of  heat  and  its  control  important? 
'2.   Illustrate  the  amount   of  heat   nt-eived  from  the  sun. 

3.  Why  do  high  altitudes  receive  more  heat  from  the  sun  than   low  ones? 

•Why  are  high  altitudes  colder? 

4.  After  the  manure  hecomes  thoroughly  decomposed  and  mixed  with  the 

soil,  what  ell'ect  will  it  have  on  temperature? 

5.  Why  should  water  vapor  raise  the  temperature  of  soil   material  more 

than  liquid  water? 
(5.  What  effect  does  color  have  on  radiation  of  heat? 

7.  Why  is  conduction  of  heat  downward   into  soil   so  slow? 

8.  Why  is  slow  germination  of  seeds  undesirable? 

!).   Is  the  temperature  of  the  soil   usually  at   the  optimum,  as  shown  in  the 
table  on  page  2fl8,  when  the  seeds  are  planted? 

10.  What   part  does  osmosis   play   in   germination? 

11.  How  does  temperature  affect  it? 

12.  What  effect   does  color  of  soil  have  on  a  cloudy  day? 

13.  How   does   the   specific   heat   of   soils   compare    with    other    substances? 

(See  tables,  page  290.) 


308  SOIL  PHYSICS  AND  MANAGEMENT 

14.  How  does  the  specific  heat  of  humus  compare  with  other  substances 

found  in  soils? 

15.  What  is  the  effect  of  evaporation  on  temperature  of  soils  ? 

16.  Explain  the  effect  of  moisture  on  specific  heat  of  soils. 

17.  Give  the  figures  in  regard  to  the  effects  of  windbreaks. 

18.  How  many  heat  units  would  be  required  to  raise  the  temperature  of  a 

cubic  foot  of  soil  five  degrees  if  it  weighs  80  pounds,  water-free,  and 
contained  20  per  cent  of  water?     Specific  heat  of  soil,  0.21. 

19.  Give  conclusion  of  experiments  of  Bouyoucos  in  table  on  page  302  with 

colored  sands. 

20.  Try  the  experiment  with  seeds  planted  in  different  colored  soils. 

21.  What  effect  did  color  have  on  different  seeds?     Why  did  melons  show 

lower  germination  ? 

22.  What  influence  does  color  have  on  very  wet  soils? 

23.  Explain  effect  of  latitude  on  temperature  of  soils. 

24.  Explain  action  of  atmosphere  in  absorption  of  heat. 

25.  What  is  the  effect  of  slope  on  temperature? 

26.  What  part  does  conductivity  play  in  temperature? 

27.  Which  will  warm  up  quicker  in  spring,  a  cultivated  soil  or  a  compact 

soil?    Why? 

28.  Why  is  dry,  loose  chalk  a  poorer  conductor  of  heat  than  quartz  powder? 

29.  Why  is  fine  sand  a  poorer  conductor  than  coarse  sand? 

30.  Why  is  wet  soil  a  better  conductor  than  dry? 

31.  For  truck  crops  do  we  need  good  or  poor  conductors? 

REFERENCES 

'Georgeson,  Agricultural  Science  I.  p.  251. 

2  Stellwaag,  Wollny,  Forsch.  der  Agricultur  Physik,  Vol.  5,  p.  210. 

8  Bouyoucos,  George  J.,  Technical  Bulletin  17,  Michigan  Station,  1913.     An 

Investigation  of  Soil  Temperature  and  Some  of  the  Most  Important 

Factors  Influencing  It,  p.  30. 
<Uloth,  Flora,  1871,  p.  185. 

"Haberlandt,  F.  Landw.  Versuchs-Stationen.  xvii,  p.  104. 
"Hall.  A.  D.,  The  Soil,  1912,  p.  123. 
7Duffi  A.  Wilmer,  A  Textbook  of  Physics,  1912,  p.  232. 

8  Bouyoucos,  G.  J.,   (see  above),  p.  12. 

9  Patten,  H.  E.  Bulletin  59,  Bureau  of  Soils,  U.  S.  D.  A.,  Heat  Transference  in 

Soils.  1909,  p.  34. 

10  Patten,  H.  E.,  (see  above) ,  p.  27. 
"Unpublished  Data,  University  of  Illinois. 
"Bouyoucos,  G.  J.,    (see  above),  p.  31. 

u  Pott.  H.  E.,  Landw.  Versuchs-Stationen,  xx,  p.  288. 
"Bouyoucos,  G.  J.,  (see  above),  p.  19. 


CHAPTER  XXIV 

SOIL  AIR  AND  AERATION 

EVERY  individual  who  has  grown  crops  knows  that  a  soil  must 
contain  air  as  well  as  water,  and  the  amount  of  one  will  vary  with 
that  of  the  other.  In  other  words,  the  air  of  a  soil  occupies  that 
space  not  occupied  by  water,  and  when  the  proportion  of  the  two 
is  about  equal  optimum  conditions  prevail. 

Use  of  Air  in  Soils. — The  most  important  element  in  soil 
air  is  oxygen.  It  is  necessary  for  the  vital  functions  that  take 
place  in  plants,  and  in  the  case  of  water-logged  soils,  in  which  the 
oxygen  is  reduced  to  a  minimum,  the  effect  can  readily  he  seen. 
Oxygen  is  necessary  for  root  respiration.  We  find  that  there  is  an 
interchange  in  the  roots,  the  carbon  dioxide  being  given  off  and  the 
oxygen  taken  in.  Oxidation,  with  or  without  the  agency  of  bacteria, 
is  necessary  for  furnishing  available  plant  food  for  the  crop.  The 
process  that  supplies  available  nitrates  is  known  as  nitrification,  and 
takes  place  through  the  agency  of  organisms.  This  is  absolutely 
necessary  in  soils,  and  if  for  any  reason  oxygen  is  prevented  from 
entering  the  soil,  or  if  the  supply  becomes  low,  the  lack  of  nitrates 
is  shown  by  the  yellowish-green  color  that  the  plant  soon  assumes. 

A  supply  of  oxygen  is  necessary  in  the  soil  for  germination  also. 
Certain  chemical  processes  take  place  in  the  seed  for  which  oxygen 
is  necessary.  In  extremely  wet  soils  seeds  germinate  very  poorly. 
Air  is  necessary  in  the  soil  for  supplying  nitrogen  to  the  nitrogen- 
fixing  bacteria,  both  symbiotic  and  non-symbiotic.  The1  carbon 
dioxide  of  the  soil  air  is  of  importance  because  of  its  effect  on  min- 
erals. These  are  slowly  decomposed  by  the  carbonic  acid  that  is 
formed,  and  plant  food  is  liberated. 

Amount  of  Air  in  Soils. — The  amount  of  air  in  soil  depends 
upon  the  porosity,  and  this  upon  the  texture.  It  would  naturally 
be  supposed  that  the  greatest  amount  of  air  would  be  in  the  soil 
having  the  highest  porosity.  This  may  not  always  be  true,  since 
soils  with  high  porosity  have  also  a  high  retentive  capacity  for 
moisture,  and  it  would  not  lie  an  unusual  thing  for  a  soil  to  retain 
so  much  water  that  it  would  reduce  the  actual  amount  of  air  present 
to  a  point  less  than  that,  held  by  sand.  (See  the  table  on  composi- 
tion of  soil  air,  page  310.) 

309 


310 


SOIL  PHYSICS  AND  MANAGEMENT 


The  structure  of  the  soil  plays  some  part  in  the  amount  of  air. 
This  is  especially  true  of  fine-grained  soils.  If  granulation  exists 
the  space  between  the  granules  will  be  largely  occupied  by  air,  even 
when  the  soil  is  well  supplied  with  water.  This  may  increase  the 
amount  of  air  so  that  it  will  compare  very  favorably  with  that  in 
sand.  The  amount  of  organic  matter  present  influences  both  the 
water  retained  and  the  porosity,  but  as  a  general  rule  it  will  in- 
crease the  amount  of  air  in  soils,  since  it  also  increases  the  granu- 
lation. The  most  important  factor  in  determining  the  amount  of 
air  in  soil  is  moisture,  which  varies  from  week  to  week.  After  a 
heavy  rain  air  may  occupy  only  a  small  fraction  of  the  total  pore 
space.  With  the  removal  of  the  water  by  percolation,  evaporation, 
and  by  roots  the  amount  of  air  increases. 

Composition  of  Soil  Air. — While  the  soil  air  contains  sub- 
stances that  are  not  found  to  any  extent  in  the  air  above,  yet  in 
general  the  same  elements  and  constituents  are  found  in  it  as  in  the 
atmosphere.  Thus  we  find  the  atmosphere  composed  of  oxygen, 
nitrogen,  and  carbon  dioxide,  with  a  few  other  elements  or  com- 
pounds. In  the  soil  air  we  find  the  same  elements  present,  but  not 
in  the  same  proportion.  The  carbon  dioxide  is  much  more  abundant 

Composition  of  Sail  Air  as  Determined  by  Boussingault  and  Lewy  1 


Character  of  soil 

Volume  in  one  acre 
of  soil  to  depth  of 
14  inches 

Composition  of  100  parts  of  soil 
air  by  volume 

Air 
(cu.  ft.) 

Carbon 
dioxide 
(cu.  ft.) 

Carbon 
dioxide 

Oxygen 

Nitrogen 

Sandy  subsoil  of  forest  .  .  . 
Loamy  subsoil  of  forest.  .  . 
Surface  soil  of  forest  
Clay  soil            .  .    .  . 

4,416 
3,530 
5,891 
10,310 

11,182 
11,182 
11,783 

11,783 
21,049 

14 
28 
57 
71 

86 
172 
257 

1,144 
772 

0.24 
0.79 
0.87 
0.66 

0.74 
1.54 
2.21 

9.74 
3.64 

i9.66 
19.01 
19.99 

19.02 
18.80 

10.35 
16.45 

7U55 
79.52 
79.35 

80.24 
79.66 

79.91 
79.91 

Soil  of  asparagus  bed  not 
manured  for  one  year.  . 
Soil     of     asparagus     bed 
freshly  manured 

Sandy  soil,  six  days  after 
manuring   

Sandy  soil,  ten  days  after 
manuring  (three  days  of 
rain)  

Vegetable  mold  compost.  . 

Per  rent  by  volume 


Ordinary  air  (above  the  surface) 


03 


20.93 


79.04 


SOIL  AIR  AND  AERATION  311 

in  soil  air  than  in  the  atmosphere,  while  the  oxygen  varies  inversely 
with  the  amount  of  carbon  dioxide,  the  nitrogen  remaining  prac- 
tically the  same. 

The  above  table  shows  the  amount  of  carbon  dioxide  in  soils 
under  different  conditions  with  the  comparative  amount  of  oxygen. 

Aeration  or  Soil  Ventilation. — Aeration  as  spoken  of  in  con- 
nection with  soils  is  an  interchange  between  the  atmosphere  and 
the  soil  air.  It  is  necessary,  first,  to  supply  the  oxygen  needed  by 
roots  and  soil  organisms;  second,  the  supply  the  nitrogen  needed  by 
nitrogen-fixing  bacteria,  and,  third,  to  remove  the  carbon  dioxide, 
an  excess  of  which  becomes  injurious  because  of  the  fact  that  it 
excludes  oxygen.  Soil  ventilation  may  be  accomplished  in  a  variety 
of  ways. 

(a)  Diffusion  is  the  mixing  of  gases  of  different  composition 
due  to  molecular  movement.     It  may  be  well  illustrated  by  filling 
a  bottle  with  carbon  dioxide,  and  although  this  gas  is  heavier  than 
ordinary  air.  yet  it'  the  bottle  is  left  unstoppered  for  a  short  time 
it  will  gradually  diffuse  into  the  surrounding  atmosphere.     As  seen 
in  the  preceding  table,  soil  air  contains  a  larger  amount  of  carbon 
dioxide  than  the  atmosphere  and  it  is  constantly,  but  slowly,  being 
removed   by  diffusion.     This   process  takes  place  more  rapidly   in 
soils  of  large  total  pore  space  than  in  those  with  large  individual 
pores,  so  that  for  heavier  soils  with  a  high  porosity  and  a  high  air 
content,  diffusion  will  take  place  more  rapidly  than  in  sandy  soils 
with  larger  pores  and  a  smaller  total  pore  space.     This  seems  con- 
trary to  the  fact  that,  sandy  soils  are  better  aerated  than  clay  soils, 
but  it  must  be  remembered  that   other  agencies  are  at    work  that 
bring  about  better  aeration  in  sandy  soils.     Compacting  a  soil,  by 
any  means,   tends  to  lessen    diffusion    because   it    lessens   the  total 
pore  space.     For  this  reason  a  soil  in  good  tilth  permits  more  rapid 
diffusion  than  one  in  poor  tilth.     Temperature  afTects  diffusion  in 
that   a   higher    temperature    produces    greater    molecular    activity. 
which  results  in  more  rapid  interchange  of  the  gases. 

(b)  Removal  of  Water. — The  removal  of  water  from  the  soil 
by  any  process  permits  air  fo  enter,  thus  bringing  into  the  soil  a 
.new  supply  of  pure  air.     As  the  water  is  carried  out   bv  drainage 
the  air  follows  downward  from  the  surface.     The  removal  of  water 
by  the  roots  of  plants  has  the  same  effect,  but   the  change   is  very 
slow. 

(c)  Changes  in  Atmospheric  Pressure. — Barometric  pressure 
is  not  constant.     Regular  changes  take  place  in  the  region  ()f  the 


312 


SOIL  PHYSICS  AND  MANAGEMENT 


prevailing  westerlies  every  three  or  four  days,  corresponding  to  the 
movement  of  "  highs  "  and  "  lows."  These  variations  amount  to 
an  average  of  about  one-half  inch  in  the  height  of  the  mercury.  At 
the  Illinois  Station  the  average  weekly  change  for  five  years  has 
been  0.45  inch.  The  minimum  during  this  time  was  0.20  inch, 
while  the  maximum  was  1.45  inches.  According  to  Boyle's  law,  a  de- 
crease in  pressure  increases  the  volume  of  a  gas,  while  an  increase  in 
pressure  diminishes  it  and  in  proportion  to  the  increase  or  decrease. 
A  difference  of  0.5  inch  in  pressure  is  equivalent  to  1/60  of  an 
atmosphere.  If  a  cubic  foot  of  soil  with  50  per  cent  of  pore  space 
has  one-half  of  this  occupied  by  air,  it  will  contain  432  cubic  inches 
of  air.  An  increase  in  pressure  of  1/60  of  an  atmosphere  will 
force  seven  cubic  inches  of  air  into  the  soil.  With  a  corresponding 
decrease  in  pressure  the  soil  air  expands,  forcing  out  the  same 
amount. 

(d)  Temperature  Changes. — When  gases  are  heated  they  ex- 
pand, and  when  cooled  they  contract.  The  amount  of  expansion  or 
contraction  is  a  definite  quantity.  Air  changes  in  volume  1/491 
for  each  change  of  one  degree  Fahrenheit,  or  1/273  for  each  degree 
Centigrade.  If  a  cubic  foot  of  soil  contains  432  cubic  inches  of 
air,  a  change  of  one  degree  will  result  in  a  change  of  approximately 
one  cubic  inch  in  volume.  During  the  growing  season  the  average 
daily  range  for  soils  to  a  depth  of  four  inches  is  about  twelve  degrees, 
as  shown  in  the  table  below. 

Range  of  Temperature  of  Plowed  and   Unplowed  Land  at  Different  Depths 
(Degrees  Fahrenheit) — Average  1912-1915  2 


Depth  

Two  inches  deep 

Four  inches  deep 

Treatment     

Plowed 

Not  plowed 

Plowed 

Not  plowed 

May  *  

12.8 
13.6 
16.0 
14.1 

11.2 
13.8 
17.7 
13.6 

10.3 
13.1 
13.2 
11.5 

9.8 
15.7 
15.6 
11.1 

June     

July  

Aueust  . 

*  Average  of  2  years. 


This  would  give  a  change  in  volume  of  about  12  cubic  inches  in 
a  cubic  foot  of  soil,  and  this  amount  would  be  expelled  during  the 
day  and  taken  in  at  night.  The  aeration  brought  about  by  changes 
in  pressure  and  temperature  produces  almost  a  complete  change  of 
the  air  in  the  surface  few  inches  of  soil  each  week. 


SOIL  AIR  AND  AERATION  313 

(e)  Tillage  is  the  most  effective  method  for  producing  a  change 
of  soil  air.    The  best  implement  for  accomplishing  this  purpose  is 
the  plow.     When  the  furrow  slice  is  turned  over  the  shearing  pro- 
duced pulverizes  the  soil  and  brings  about  a  complete  change  of  air 
in  all  except  the  granules,  and  breaking  the  soil  up  brings  al>out  a 
much  better  chance  for  a  change  in  these.     Any  form  of  tillage, 
however,  will  materially  aid  aeration.     Plowing  cloddy  ground  ac- 
complishes the  least.     When  these  clods  are  thoroughly  pulverized 
much  better  interchange  takes  place,  and  this  is  one  of  the  groat 
advantages  of  thorough  pulverization  of  the  soil. 

(f)  Wind  Movement. — The  wind  as  a  general  rule  moves  in 
gusts,  and  these  passing  over  a  field  have  a  tendency  to  draw  out 
the  air  from  the  soil  and  aid  aeration  to  some  extent  in  this  way. 
Any  exact  determination  of  this  effect  of  wind  would  be  very  diffi- 
cult, yet  it  is  probable  that  on  soils  having  large  air  spaces,  such 
as  cloddy  or  sandy  ones,  this  plays  quite  an    important  part   in 
aeration. 

Water-logged  Soil. — Many  soils  which  have  imperfect  drain- 
age due  to  a  high  water  table  or  an  impervious  stratum  may  con- 
tain such  a  large  amount  of  water  as  to  exclude  the  air,  resulting 
in  a  very  serious  condition,  so  far  as  the  vital  soil  activities  arc  con- 
cerned. The  remedy,  of  course,  is  drainage,  and  the  drainage 
should  be  sufficiently  complete  so  that  a  heavy  rain  fall  will  not 
saturate  the  soil  for  any  length  of  time.  If  the  water  table  is  two 
or  three  feet  from  the  surface,  a  heavy  rain  may  raise  this  sufficiently 
to  injure  the  crop  unless  the  soil  is  thoroughly  drained.  Many 
systems  of  drainage  have  not  been  sufficient  to  lower  the  water  table 
rapidly  and  the  result  is  that  in  wet  seasons  the  crop  is  badly 
damaged.  Even  in  moderately  wet  seasons  the  crop  in  the  lower 
places  where  the  water  table  is  near  the  surface  will  assume  a 
yellowish-green  color,  indicating  that  injury  is  being  done  by  lark 
of  aeration. 

Running  Together. — Soils  that  are  deficient  in  organic  matter 
are  in  condition  to  be  easily  puddled,  especially  the  fine  and  medium 
grained  ones.  A  heavy  rain  may  be  sufficient  to  do  this.  The 
beating  of  the  rain  drops  breaks  the  granules  into  individual  par- 
ticles that  render  the  surface  impervious  both  to  air  and  water,  thus 
cutting  off  the  supply  of  air.  If  this  condition  continues  for  any 
length  of  time,  the  crop  may  be  retarded  in  its  growth  and  be- 
come of  a  greenish-yellow  color,  indicating  nitrogen  starvation. 
The  remedy,  of  course,  is  tillage  for  breaking  the  crust  and  aerating 


314  SOIL  PHYSICS  AND  MANAGEMENT 

the  soil.  If  a  heavy  soil  or  a  soil  rich  in  organic  matter  should 
become  puddled  in  this  way  by  a  shower,  upon  drying,  shrinkage 
cracks  will  be  formed  through  which  air  may  enter.  Tillage  would 
not  be  so  necessary  in  that  case.  In  light  sandy  soils  this  puddling 
will  not  take  place. 

QUESTIONS 

1.  Give  uses  of  air  in  soils. 

2.  What  are  some  indications  by  the  plant  that  oxygen  is  deficient? 

3.  Upon  what  does  the  amount  of  air  that  the  soil  will  contain  depend? 

4.  What  causes  variations  in  the  composition  of  soil  air? 

5.  In  table  on  page  310  what  is  the  average  amount  of  nitrogen? 
G.  How  does  this  compare  with  the  normal  amount  in  air? 

7.  Define  aeration. 

8.  Why  is  it  necessary? 

9.  What  is  diffusion  ?    Illustrate. 

10.  What  effect  does  porosity  have  on  diffusion  ? 

11.  How  does  temperature  affect  it? 

12.  How  does  removal  of  water  aid  diffusion? 

13.  How  much  change  in  atmospheric  pressure  in  a  week? 

14.  What  is  Boyle's  law? 

15.  What  part  of  an  atmosphere  is  represented  by  a  change  of  0.45  inch 

of  pressure? 
1(>.  How  does  atmospheric  change  effect  aeration? 

17.  Explain  the  effect  of  temperature  changes  on  aeration? 

18.  Give  average  change  for  the  four  months  for  each  depth  and  for  each 

treatment. 

19.  How  much  of  a  change  in  volume  would   occur   for   each   if  the  soil 

volume  were  one-fourth  air? 

20.  Explain  the  effect  of  tillage  on  aeration. 

21.  Give  effect  of  wind  movement. 

22.  What  is  a  water-logged  soil  ? 

23.  How  may  it  be  avoided? 

24.  Why  is  it  detrimental  to  the  crop? 

25.  What  effect  does  running  together  have  on  aeration  ? 

REFERENCES 

', Johnson,  S.  W.,  How  Crops  Feed,  1891,  p.  219. 
*  Unpublished  Data,  University  of  Illinois. 


CHAPTKK    XXV 

SOIL  ORGANISMS 

THE  soil  contains  large  numbers  of  organisms,  both  plants  and 
animals  of  various  kinds,  that  act  upon  botli  the  organic  and  min- 
eral constituents  of  the  soil.  They  produce  changes,  many  of  which 
are  highly  beneficial,  while  others  are  detrimental.  For  convenience 
they  may  be  divided  into  macro-organisms,  such  as  rodents  and  in- 
sects, and  micro-organisms,  those  of  microscopic  sixe,  such  as  furgi 
and  bacteria. 

MACRO-ORGANISMS 

1.  Rodents. — Large  numbers  of  rodents,  such  as  squirrels,  rats, 
mice,  prairie  dogs  and  gophers,  have  the  habit  of  burrowing  in  the 
soil,  thus  facilitating  the  action  of  certain  agencies.     These  carry 
soil  upward  and  a  more  thorough  mixing  of  the  surface  and  sub- 
soil is  thus  brought  about.     Later  these  openings  are  iilled  with 
surface   soil.      Much   vegetable   matter  also   is   carried    into   these 
burrows,  which  helps  in  decomposition  of  the  minerals  with  which 
it  comes  in  contact.    Aeration  and  percolation  are  aided  by  the  work 
of  these  animals.     It  is  interesting  to  note  that  very  few  burrowing 
rodents  are  found  in  regions  of  tight  clav  subsoils. 

2.  Insects. — A  great  many  insects  live  in  the  earth  during  their 
larval  state  or  even  the  whole  of  their  lives.     The  larval  stage  of  in- 
sects, is   their  most   active   period.      They   are   constantly   working 
their  way  through  the  soil  and  in  this  way  aid  aeration  and  drainage. 
Seventeen-year   locusts  are   very  abundant    in   soils    in   some   local 
areas.     Over  r>00  e\uvi;e.   or  cast-oil"  shells,  of  these   insects  were 
counted    upon   a   hawthorn    bush    not   over   three    feet    high.      Ants 
work  up  their  hills,  tilling  them  with  vegetable  matter,  and  when 
they  are  abandoned  form  very  rich  spots  of  soil. 

3.  Worms. — Earthworms    are    most    common    organisms    and 
are  found  in  medium  and  heavy  soils  of  humid  areas  that  are  well 

'supplied  with  organic  matter.  They  do  not  seem  to  be  so  abundant 
in  acid  soils,  evidently  preferring  those  containing  some  limestone. 
They  do  not  live  in  sands,  light  sandy  loams,  arid  or  semi-arid 
soils.  They  aid  in  aeration  and  their  burrows  improve  drainage. 
They  pass  large  quantities  of  soil  through  their  bodies.  The  min- 

315 


316  SOIL  PHYSICS  AND  MANAGEMENT 

erals  are  acted  upon  by  the  acids  of  the  alimentary  canal,  producing 
chemical  changes  resulting  in  the  liberation  of  plant  food.  They 
carry  large  amounts  of  soil  from  the  subsurface  and  subsoil  and 
deposit  it  on  the  surface  of  the  ground,  where  it  may  be  seen  as 
casts,  especially  in  the  morning  after  a  rain.  Darwin  states  that 
where  earthworms  abound  the  amount  brought  by  them  forms  a 
layer  from  0.1  to  0.2  inch  in  thickness  each  year.  This  amounts  to 
from  15  to  30  tons  per  acre.  Some  comparative  experiments  have 
been  conducted  which  show  that  earthworms  increase  the  yield  of 
crops. 

4.  Plants. — The  soil  is  modified  to  a  large  extent  by  the  roots 
of  all  plants,  whether  large  or  small.  The  short-lived  annuals  and 
biennials  have  the  greater  effect,  because  new  roots  are  formed  every 
one  or  two  years.  The  roots  of  perennial  prairie  grasses  are  great 
factors  in  modifying  soil  because  of  their  great  abundance  and 
deep  penetration.  While  most  of  the  roots  of  trees  and  shrubs  live 
for  years,  yet  many  die  every  season.  Eoots  of  all  plants  add  some 
organic  matter  to  the  soil,  but  they  have  another  important  effect. 
They  make  the  soil  more  porous  after  they  decay  and  thus  improve 
aeration  and  drainage.  Frequently  when  timber  spreads  over  a 
prairie  area  having  a  tight  clay  subsoil  the  ultimate  effect  of  the 
roots  is  to  lessen  the  impervious  character  of  the  subsoil  so  that 
drainage  takes  place  with  much  less  difficulty. 

Many  fungi  live  on  and  in  the  soil  and  affect  it  to  some  extent. 
Some  aid  in  the  early  decomposition  of  vegetable  matter.  Others 
are  diseases,  such  as  some  smut  and  scab.  Others  live  in  sym- 
biotic relation  to  certain  higher  plants.  These  through  the  agency 
of  large  numbers  of  hypha?  or  fungi  rootlets,  called  michoriza,  trans- 
fer the  food  to  the  companion  plant. 

MICRO-ORGANISMS 

The  group  of  micro-organisms,  consisting  of  bacteria,  fungi, 
protozoa,  algae  and  yeasts,  is  of  special  importance  in  soils.  They 
aid  in  the  transformation  of  the  vegetable  and  animal  remains  into 
the  humus-like  residue,  which  really  constitutes  part  of  the  soil. 
They  carry  on  many  other  operations  that  benefit  soils  chemically 
and  to  some  extent  physically.  However,  the  physical  condition  of 
soils  and  the  phenomena  that  occur  in  them  which  influence  the 
work  and  development  of  these  micro-organisms  are  so  important 
that  they  merit  considerable  attention.  How  the  farmer  may  in- 


SOIL  ORGANISMS  317 

fluence  the  work  of  these  organisms  is  a  question  that  every  one 
interested  in  agriculture  should  know.  The  micro-organisms  in  the 
soil  are  of  two  general  kinds,  injurious  and  beneficial. 

1.  Injurious  Organisms. — After  a  soil  has  been  cropped  for  a 
number  of  years  it  is  frequently  found  to  contain  numbers  of  or- 
ganisms of  various  kinds,  some  of  which  are  not  only  of  no  benefit 
to  the  crop,  but  are  actually  injurious.     The  number  and  char- 
acter of  these  depend  largely  upon  the  crops  grown  and  the  rota- 
tion practiced.     A  single  crop  system  is  likely  to  encourage  the  de- 
velopment of  organisms  injurious  to  that  crop.    Hence  a  rotation  is 
advisable. 

Some  of  these  are  the  wilt  of  cotton,  flax,  cowpeas,  probably 
clover  sickness,  the  scab  of  potatoes,  the  rots  of  many  plants.  These 
perish  when  by  rotation  they  are  deprived  of  their  host  plants  for 
a  few  years. 

2.  Beneficial  Organisms. — The  heneficial  organisms  comprise 
a  considerable  number  of  forms,  but  the  group  of  bacteria  is  of 
special  importance.      It  would  be  impossible  to.  grow  crops  with- 
out these.     They  are  the  farmer's  best  friends.     They  aid  him  in 
getting  plant  food  into  the  soil  in  the  process  of  nitrogen  fixation 
and  are  of  vital  importance  in  making  plant  food  available,  as  in 
the  process  of  nitrification. 

(a)  Fixation  of  Nitrogen. — Some  bacteria  in  the  soil  live  in 
symbiotic  relation  with  legumes,  producing  nodules  or  tubercles  upon 
the  roots.    Their  function  as  they  grow  in  this  connection  is  to  take 
nitrogen  from  the  soil  air  and  put  it  into  the  plant,  in  this  way 
storing  up  or  fixing  nitrogen.    These  organisms  live  in  this  relation- 
ship with  legumes  and  this  explains  the  importance  of  this  class  of 
plants  to   the   farmer.     Turning  under  the   legumes   enables  the 
fanner  to  get  a  supply  of  nitrogen  into  the  soil  with  little  expense 
and  in  a  form  that  is  readily  available  to  other  plants  which  can 
use    only   soil    nitrogen.      In    general    each    legume    has    its    own 
special  bacteria. 

Another  class  of  bacteria  known  as  A/otobacter  have  the  power 
of  fixing  nitrogen  in  the  soil  directlv  or  independent  of  any  other 
plant.  To  what  extent  this  is  done  is  not  definitely  known,  but  no 
doubt  it  is  of  sufficient  consequence  to  justify  careful  consideration 
in  producing  favorable  conditions  for  their  activity. 

(b)  Nitrification. — The  nitrogen  of  soil  organic  matter  cannot 
he  used  directlv  bv  our  crops.     Tt  must  first  he  changed  into  some 
readily  soluble  form,  usually  nitrates.    Some  crops,  such  as  rice  and 


318  SOIL  PHYSICS  AND  MANAGEMENT 

potatoes  and  possibly  others,  may  use  more  or  less  of  it  in  the  form 
of  ammonium  compounds.  By  far  the  larger  part  is  taken  up  by 
plants  as  nitrates.  The  soil  nitrogen  must  be  changed  to  this  form. 
The  process  of  nitrification  is  the  changing  of  the  nitrogen  of  soil 
organic  matter  into  nitrates,  and  is  accomplished  through  the  ac- 
tion of  certain  classes  of  bacteria.  The  steps  in  the  process  are  as 
follows : 

(1)  Ammonification,  in  which  the  organic  matter  is  decom- 
posed by  bacteria  and  the  nitrogen  changed  into  ammonia  or  com- 
pounds of  ammonia. 

(2)  Nitrification  proper,   which  consists  of  the  formation  of 
nitrous  acid  or  nitrites  from  the  ammonia  or  ammonium  com- 
pounds and  the  subsequent  change  to  nitric  acid  or  nitrates.     This 
is  essentially  oxidation.    The  nitrous  and  nitric  acids  unite  with  a 
base  of  the  soil.    As  calcium  is  one  of  the  most  common  and  readily 
available  bases,  calcium  nitrate  is  usually  formed. 

DISTRIBUTION    AND    CONDITIONS 

1.  Distribution. — The  bacteria  concerned  in  nitrification  are 
very  widely  distributed  in  all  kinds  of  soil,  with  the  possible  excep- 
tion of  swamp  or  long  flooded  soils.  They  are  much  more  abundant 
in  soils  containing  limestone  than  in  strongly  acid  ones.  The  sym- 
biotic bacteria  for  legumes  are  found  practically  everywhere,  but 
not  the  specific  forms  for  all  legumes.  The  bacteria  for  alfalfa  are 
very  widely  distributed  over  western  regions  of  the  United  States, 
but  in  the  eastern  region  inoculation,  which  is  the  process  of  sup- 
plying the  proper  bacteria,  is  necessary.  The  same  is  true  of  many 
other  legumes.  Wild  legumes  sometimes  carry  the  same  bacteria 
as  our  cultivated  ones. 

The  number  of  bacteria  changes  with  the  type  of  soil.  On  the 
same  kind  of  soil  the  number  of  bacteria  varies  with  the  degree  of 
fertility,  the  tilth,  and  the  rotation  practiced. 

In  vertical  distribution  the  bacteria  increase  in  number  from 
the  surface  downward  for  four  to  six  inches  and  then  decrease  rap- 
idly with  depth  and  are  found  several  feet  below  the  surface  only 
as  they  are  carried  downward  by  percolating  water.  The  zone  of 
greatest  number  of  bacteria  is  from  five  to  six  inches  beneath  the 
surface,  but  it  will  vary  somewhat  with  the  soil  type,  being  a  little 
deeper  in  well-aerated  soils.  The  optimum  conditions  of  tempera- 
ture, moisture  and  aeration  are  found  at  this  depth.  The  following 


SOIL  ORGANISMS 


319 


table  gives  the  number  of  bacteria  at  various  depths  under  different 
systems  of  cropping  at  the  Iowa  Station : 

Bacteria  per  Gram  of  Air-Dry  Soil 1 — Rotations 


Corn,  oats, 

Depth  of  sampling 

Continuous  corn 

Corn,  corn,  oats, 
and  clover 

clover  turned 
under  first 

C'orn,  oats, 
clover 

season 

4  inches 

1,752,000 

2,912,000 

4,148,250 

4,164,000 

8  inches 

1,248,250 

2,027,000 

3,591,000 

2,943,750 

12  inch«s 

546,000 

560,500 

1,167,750 

907,500 

16  inches 

298,250 

3  16,  (XX) 

348,250 

315,000 

20  inches 

153,500 

256,000 

223,000 

155,750 

24  inches 

93,850 

89,225 

108,750 

91,825 

30  inches 

48,500 

49,025 

60,125 

53,775 

30  inches 

31,600 

32,475 

37,625 

34,800 

It  will  be  noted  that  the  number  of  bacteria  at  four  inches  in 
depth  is  greatest  in  the  rotation  which  brings  the  clover  crop  on 
the  land  more  frequently.  The  difference  is  very  striking  when 
compared  with  continuous  corn. 

The  Kansas  Station  found  that  the  number  varied  directly  with 
the  fertility  of  the  soil. 

'3.  Conditions  for  Development. —  It  is  generally  known  that 
most  plants  require  very  favorable  conditions  for  their  growth,  such 
as  food,  moisture,  heat,  air,  light,  and  the  physical  condition  of  the 
soil.  The  same  conditions  that  are  favorable  to  higher  plants  are 
favorable  for  the  activity  of  bacteria,  with  the  exception  of  light. 

(a)  Moisture. — Bacterial    activity    involving   chemical    change 
ceases  in  dry  soil.     The  other  extreme,  a  water-logged  soil,  is  almost 
equally  inhibitive  of  the  action  of  bacteria.     When  a  soil  has  ap- 
proximately half  of  its  air  space  filled  with  moisture  the- conditions 
are  most  favorable  for  bacterial  activity  and  their  growth  is  most 
rapid. 

(b)  Food. — Organic  matter  is  a  very  important   food  for  most 
bacteria,  but  some  of  the  beneficial  organisms  obtain  their  supply 
of  carbon  from  carbon  dioxide.     They  develop  in  great  numbers  in 
drained    soils    having    an    abundance    of    organic    matter.      Small 
amounts  of  mineral    food   are   required,  but   soils  usually  contain 
sufficient  quantities  for  the  use  of  these  organisms.     Soluble  organic 
matter  in  considerable  quantities  tends  to  inhibit  nitrification.     Xor- 
mal  soils  contain  very  little.     Large  amounts  of  sewage  are  not  de- 
sirable on  land  because  it  furnishes  soluble  organic  matter. 


320  SOIL  PHYSICS  AND  MANAGEMENT 

(c)  Temperature. — The  optimum   temperature  for  bacterial 
activity  lies  between  65  and  95  degrees  F.  (18  and  35  degrees  C.). 
It  diminishes  as  the  temperature  increases,  and  at  130  to  140  degrees 
F.  action  ceases  and  many  are  killed.    Below  65  degrees  F.  the  bac- 
teria become  less  active  and  cease  at  32  degrees  F.,  although  they 
are  not  killed.    Early  tillage,  drainage  and  a  dark  color  raise  tem- 
perature and  encourage  bacterial  action. 

(d)  Aeration. — Bacteria  are  divided  into  two  general  classes, 
aerobic,  those  requiring  oxygen  for  their  growth  and  activity  or 
work,  and  the  anaerobic,  which  require  no  oxygen.    Aeration  is  very 
essential  to  the  first  group.     Since  nitrification  is  the  most  im- 
portant work  of  bacteria  in  soils  the  amount  of  nitrates  produced 
may  be  taken  as  a  measure  of  their  activity.     Experiments  show 
that  in  the  absence  of  oxygen  not  only  were  no  nitrates  formed,  but 
the  nitrates  present  were  reduced  with  evolution  of  free  nitrogen. 
When  six  per  cent  of  oxygen  was  present  the  amount  of  nitrates 
formed  was  double  what  it  was  with  1.5  per  cent.2 

(e)  Reaction. — Soils  giving  acid  reactions  are  not  very  favor- 
able to  the  work  of  bacteria.     They  are  more  active  in  soils  that 
are  neutral  or  slightly  alkaline.     The  nitrifying  bacteria  produce 
nitrous  and  nitric  acids,  which  tend  to  inhibit  their  action.     If 
bases  are  present  in  the  soil  these  will  unite  with  the  acids  pro- 
duced, thus  keeping  the  soil  neutral  or  alkaline,  and  in  good  con- 
dition for  their  work.     Limestone  should  be  applied  to  the  soil  to 
neutralize  the  acidity. 

Crops  growing  on  water-logged  soils  are  usually  yellow.  This 
is  due  to  a  lack  of  available  nitrates.  The  water  excludes,  the  air 
and  the  bacteria  cannot  do  their  work.  The  same  conditions  exist 
when  a  soil  in  poor  tilth  runs  together  and  bakes,  forming  a  crust 
impervious  to  air.  When  aeration  is  produced  by  cultivation 
nitrates  are  formed  and  a  crop  such  as  corn  resumes  its  normal  dark 
green  color. 

Another  important  function  of  aeration  is  to  remove  the  carbon 
dioxide  of  the  soil  air.  This  is  necessary  because  it  excludes  oxygen. 
In  the  process  of  nitrification  carbon  dioxide  is  formed.  Tillage  is 
the  best  means  of  bringing  about  aeration.  Deherain  3  conducted  an 
experiment  which  shows  the  effect  of  tillage  on  aeration  and  con- 
sequently upon  the  action  of  nitrifying  bacteria.  A  quantity  of 
soil  was  thrown  upon  the  floor  and  worked  daily  for  six  weeks.  At 
the  end  of  this  time  the  stirred  soil  contained  23.7  times  as  much 
nitric  nitrogen  as  the  soil  not  disturbed.  "  Nitrate'  farming  "  as 


SOIL  ORGANISMS 


321 


formerly  practiced  is  aii  application  of  this  principle.  The  soil  rich 
in  organic  matter  was  stirred  and  moistened  to  develop  a  large 
amount  of  nitrates,  which  were  then  leached  out  and  used  for  com- 
mercial purposes,  principally  in  the  manufacture  of  gunpowder. 

Effect  of  Different  Amounts  of  Lime  Upon  the  Number  of  Bacteria  per  Gram 

of  Dry  Soil 4 


Treatment 

Number  of 
bacteria  at 
beginning  of 
experiment 

Number  of 
bacteria  after 
7  week* 

None                  

504,000 

417,000 

1000  pounds  lime  per  acre  

7  IS,  (XX) 

1,551,000 

2(KM)  {K)unds  lime  per  acre 

657,000 

1,322  000 

4000  pounds  lime  per  acre  

480  (XX) 

5,571,000 

This  table  shows  the  effect  of  lime  carbonate  upon  the  number 
of  bacteria  and  indicates  a  much  greater  development  for  the  higher 
lime  content.  An  excess  of  lime  is  not  injurious,  as  in  the  case 
of  some  other  alkaline  carbonates  as  shown  in  the  next  table. 

Effect  of  Alkaline  Carbonate  Upon  Amount  of  Nitrates  Produced  * — 
1,(XK)  Grams  of  Acid  Soil 


Treatment 


Nitrates  formed 


None 
1  gram  K2CO3 
2  gram  K  >CO3 
3  gram  K.CO3 
4  pram  KsCO3 
5  gram  K2CO3 

70  milligrams 
160  milligrams 
230  milligrams 
250  milligrams 
130  milligrams 
73  milligrams 

(f)  Physical  Composition. — Certain  physical  phenomena  upon 
which  bacteria  depend  for  their  greatest  activity  and  development 
take  place  better  in  the  medium-grained  soils  than  in  very  fine  ones. 
Very  sandy  soils  are  well  aerated,  but  usually  do  not  contain  suf- 
ficient  moisture   and    food.      Granulation    overcomes   this    in    the 
heavier  soils  to  some  extent.     Kven  with  this  aid  aeration  and  the 
moisture  conditions  are  not  so  favorable  and  nitrification  is  usually 
slower.     Tillage  is  more  essential  for  these  soils.     Where  limestone 
is  absent  heavy   soils   may   be   unfavorable  for  bacterial   activity. 
Limestone  aids  in  granulation  and  thus  indirectly  in  aeration. 

(g)  Light. — Direct  sunlight  greatly  weakens  or  even  kills  bac- 
teria.    The  /one  of  greatest  numbers  is  sufficiently  deep  so  that 

21 


322 


SOIL  PHYSICS  AND  MANAGEMENT 


sunlight  does  not  penetrate  to  it.  All  inoculating  material  and 
inoculated  seed  should  be  kept  from  direct  sunlight,  because  of  its 
drying  effect. 

Loss  of  Nitrates. — Soils  lose  nitrates  in  three  ways:  by  leach- 
ing, denitrification  and  by  the  growth  of  weeds  or  other  plants 
foreign  to  the  crop. 

1.  Leaching. — The  greatest  loss  of  nitrates  is  through  leach- 
ing. Nitrates  are  very  readily  soluble  in  water.  During  rains  those 
formed  in  manure  heaps  or  soil  may  he  carried  into  drainage  sys- 
tems and  lost.  That  this  does  occur  to  a  considerable  extent  is 
shown  by  analysis  of  drainage  waters. 

Deherain  collected  drainage  waters  from  cement  tanks  with 
results  as  given  in  the  following  table.  The  tanks  had  been  filled 
several  years  before. 

Loss  of  Nitrates  by  Leaching  6 


Cropping 

Drainage,  inches 

Nitrogen  as  nitric 
nitrogen,  pounds 
per  acre  in 
drainage 

Fallow,  no  cultivation  

11.2 

186.7 

Rye  grass  

7.8 

2.28 

Oats  

7.3 

7.37 

Maize  

6.9 

21.60 

Wheat  followed  by  vetches  

6.6 

12.60 

Wheat  

7.5 

28.70 

Fallow,  hoed  

11.5 

196.56 

Fallow,  no  cultivation     

11.2 

158.00 

Fallow,  hoed  and  rolled     .       .    . 

11.2 

183.20 

Vine  

7.5 

36.20 

Sugar  beet  

7.2 

0.27 

The  rainfall  during  the  season  was  28.8  inches.  It  is  very  inter- 
esting to  note  the  effect  of  the  crop  on  the  amount  of  drainage  and 
also  on  the  nitrogen  removed  with  the  water.  Catch  crops  are  of 
value  in  preventing  loss  of  nitrogen  in  this  way.  Even  weeds  may 
serve  as  a  catch  crop  after  the  main  crop  is  removed. 

Fallowing  (leaving  land  without  a  crop  and  cultivating  during 
summer)  in  humid  areas  is  a  very  expensive  operation  and  should 
never  be  practiced.  It  will  not  be  necessary  if  the  organic  matter  is 
properly  maintained.  Fallowing  is  resorted  to  when  the  active 
organic  matter  has  been  largely  removed  by  cropping  and  some 
special  means  must  be  taken  to  render  the  less  active  form  avail- 
able. This  is  accompanied  with  too  much  loss  of  the  most  expen- 
sive plant  food,  nitrates  in  soils,  to  be  profitable.  In  the  above  table 


SOIL  ORGANISMS  323 

the  loss  of  nitrates  by  leaching  from  fallowed  land  is  181.1  pounds 
per  acre,  while  the  cropped  land  shows  an  average  loss  of  15.G 
pounds,  or  only  one-tenth  the  amount  of  the  fallowed. 

2.  Denitrification. — Nitrification  is  an  oxidation  process,  while 
denitrification  is  one  of  reduction  or  deoxidation  by  which  nitrates 
are  broken  down  and  free  nitrogen  given  oil".  In  other  cases  the 
change  may  be  such  as  to  form  nitrites  or  ammonia.  In  the  latter 
the  nitrogen  may  not  be  lost  from  the  soil  by  it.  It  takes  place  in 
soils  when  poor  aeration  results  in  a  deficiency  of  oxygen,  as  in 
heavy,  compact,  puddled,  or  water-logged  soils.  Manure  contains 
large  numbers  of  denitrifying  bacteria  and  extremely  heavy  appli- 
cations of  coarse  manure  may  result  in  some  loss  through  the  action 
of  these  organisms. 

QUESTIONS 

1.  What  kinds  of  organisms  are  found  in  the  soil? 

2.  What  are  macro-organisms?     Micro-organisms? 

3.  (iive  the  effects  of  rodents  on  the  soil. 

4.  (Jive  the  work  of  insects  in  soils. 

5.  Where  are  worms  most  abundant? 

(i.  What  work  do  they  perform  in  soils? 

7.  (Jive  Darwin's   statements   of   the  amount  of  material   brought  to   the 

surface. 

8.  (Jive  the  effects  of  plants  on  soils. 

J).  What  is  the  work  of  micro-organisms  in  soils? 

10.  What  part  do  fungi  play? 

11.  Tell  about  the  injurious  forms. 

12.  (Jive  the  two  methods  of  fixation  of  nitrogen. 

13.  What  is  nitrification? 

14.  Tell  about  the  steps  in  the  process. 

!;">.  Where  are  soil  bacteria  most  abundant? 
1(5.  What  about  the  distribution  of  bacteria? 

17.  How  do  the  number  of  bacteria  vary? 

18.  How  are  they  distributed  vertically? 

10.  What  effect  do  different  systems  of  cropping  have? 

20.  What  two  general  classes  of  bacteria  '.' 

21.  (Jive  the  characteristics  of  each. 

22.  Of  what  use  is  aeration  to  bacteria? 

23.  (Jive  the  experiment  by   Hall. 

24.  What  was  "  nitre  farming"  ? 

25.  Why  should  bacterial  activity  almost  cease  in  soils  of  extreme  moisture 

content? 

20.  What    temperatures    ar     nest    for    the    work    of    bacteria?      What    are 
detrimental  ? 

27.  What  are  t'-e  foods  of  bacteria? 

28.  What  part  does  the  reaction  «>f  the  soil   play   in   bacterial   activity? 
2!).   What  conclusion   do  you   reach    from   tables  on   page  321? 

30.  Why    should    the    physical    composition    of    the    soil    affect    bacterial 

activity? 

31.  dive  the  effect  of  sunlight  on  bacteria. 

32.  How  are  nitrates  lost  from  soils? 


324  SOIL  PHYSICS  AND  MANAGEMENT 

33.  Give  conclusions  from  table  on  page  322. 

34.  What  effect  did  cropping  have  on  drainage? 

35.  What  is  fallowing? 

36.  Why  should  there  be  such  a  large  loss  of  nitrates  from  the  fallowed 

land? 

37.  What  is  denitrification  ? 

38.  Under  what  conditions  does  it  occur? 

REFERENCES 

1  Brown,  P.  E.,  Research  Bulletin  8,  Iowa  Station,  Bacteria  at  Different 
Depths  in  Some  Typical  Iowa  Soils,  p.  280. 

*  Schldsing,  Compt.  Kend.  Academy  of  Science,  Paris,  vol.  Ixxvii,  pp. 
203-253. 

*Deherain,  Compt.  Rend.  Academy  of  Science,  Paris,  vol.  cvi,  1893,  pp. 
1091-97. 

4  Chester,  Frederick  E.,  Bulletin  98,  Department  of  Agriculture,  Penn- 
sylvania, 1902,  p.  25. 

"Dumont,  Compt.  Rend.  Academy  of  Science,  Paris,  vol.  cxxv,  1897,  pp. 
469-72. 

•Deherain,  Noted  by  Hall,  A.  D.,  The  Soil,  1912,  p.  228. 


CHAPTER  XXVI 

TILLAGE 

IN  the  time  of  Jethro  Tull  (1GT4-1741)  the  present  theory  of 
plant  nutrition  liad  not  been  advanced,  and  this  well-known  hus- 
bandman frequently  made  the  .statement  that  "tillage  is  manure." 
While  his  theory  was  wrong,  yet  his  practice  was  right.  He  believed 
that  the  object  of  fining  the  soil  was  to  enable  the  plant  to  take  up 
the  small  particles  for  growth.  The  practice  resulting  from  this 
belief  was  as  good  as  would  have  been  brought  about  had  the  real 
theory  of  plant  nutrition  been  known.  We  know  now  that  the  pur- 
pose of  tillage  is  not  to  furnish  fine  particles  of  soil  for  the  plant. 
However,  tillage  accomplishes  a  number  of  objects,  many  of  which 
are  closely  related  to  the  production  of  plant  food  for  the  crop. 

Tillage  is  the  practice  of  working  the  soil  for  the  purpose  of 
bringing  about  more  favorable  conditions  for  germination  and  plant 
growth.  All  operations  that  affect  the  soil  by  stirring,  inverting, 
fining,  or  firming  are  included  in  tillage.  The  most  common  are 
plowing,  harrowing,  rolling,  and  cultivating. 


THE  OIWECTS  OF  TILLAGE 

1.  Pulverizing  and  Loosening  the  Soil. — The  natural  ten- 
dency of  soils  is  to  become  compact,  principally  through  the  action 
of  rain,  and  in  spite  of  the  influence  of  the  roots  of  plants  and  the 
organisms  in  the  soil  whose  tendency  is  to  keep  the  soil  loose  and  in 
good  tilth.     It  is  necessary,  then,  to  stir  the  soil  to  allow  the  funda- 
mental processes  that  are  vital  to  crops  to  take  place.     On  the  brown 
silt  loam  of  the  corn  belt  a  rotation  of  corn,  corn,  oats,  and  clover 
was  practiced.     The  soil  was  plowed  preceding  the  oat  crop  and  at 
no  other  time.    The  two  crops  of  corn  were  planted  in  the  unplowed 
soil,  and  a  yield  of  .'J5.'»  bushels  per  acre  was  produced  as  a  nine- 
year  average.     The  plowed  land  produced   l.'i.T  bushels  more.1 

2.  Turning  under  vegetable  matter  and  incorporating  it  and 
other  fertilizers  with  the  soil.     In  our  farm  practice  it  is  necessary 
to  maintain  the  supply  of  organic  matter,  and  this  can  l>e  done  only 
by  incorporating  large  quantities  of  vegetable  material  in  the  soil. 
When  plants  die  and  fall  to  the  surface  of  the  ground,  unless  some 

325 


326  SOIL  PHYSICS  AND  MANAGEMENT 

means  is  taken  for  mixing  them  with  the  soil  they  decompose 
almost  entirely,  leaving  little  more  than  the  ash  of  the  plant  to  mix 
with  the  soil.  Even  if  this  mixing  were  not  necessary  the  vegetable 
material  would  interfere  with  cultivation  if  left  on  the  surface. 
The  plow  is  the  best  implement  for  covering  all.  organic  material, 
such  as  crop  residues,  weeds,  and  farmyard  manure. 

3.  Killing  Weeds. — A  most  important  object  of  tillage  is  kill- 
ing weeds.    We  see  demonstrations  everywhere  of  the  fact  that  ordi- 
nary crops  amount  to  very  little  when  in  competition  with  weeds. 
A  weed  is  a  better  forager  than  a  cultivated  plant,  and  hence  will 
deprive  it  of  both  moisture  and  food,  and  it  is  necessary  for  suc- 
cessful crop  production  that  the  weeds  be  destroyed.    Tillage  is  the 
best  means  so  far  devised  for  accomplishing  this  purpose.    In  some 
cases,  however,  sprays  have  been  used  successfully,  and  if  sprays 
could  be  found  which  would  not  injure  the  crop,  but  would  kill  the 
weeds,  there  is  no  question  but  that  much  of  our  tillage  could  be 
dispensed  with. 

4.  Storing   and    Conserving    Moisture. — Plants    require    an 
abundant  supply  of  moisture  for  their  germination  and  growth.    In 
nearly  all  climates  through  uneven  distribution  of  rainfall  the  neces- 
sity exists  for  storing  moisture  in  the  soil  when  it  can  be  obtained 
and  for  conserving  this  for  the  use  of  the  crop  later.     The  early 
preparation  of  the  soil  by  loosening  and  compacting  slightly  is  the 
best  means  for  storing  the  supply  of  this  for  future  use.    Loosening 
the  soil  allows  rapid  absorption  with  little  run-off,  while  stirring 
the  surface  soil  later  prevents  any  excessive  loss  through  evapora- 
tion.   Of  these  two  under  ordinary  humid  conditions,  the  prepara- 
tion of  the  soil  for  storing  the  moisture  is  of  much  more  importance 
than  subsequent  tillage  for  retaining  it  when  a  crop  is  growing. 
Previous  to  the  planting  of  the  crop  the  soil  should  be  kept  stirred. 

5.  Compacting    the    Soil. — It    frequently  becomes  necessary 
after  a  soil  has  been  plowed  to  compact  it  in  order  to  close  any 
large  air  spaces  that  may  exist  in  the  plowed  soil  and  also  bring  the 
furrow-slice  in  close  contact  with  the  soil  beneath  it  so  that  capillary 
action  may  not  be  cut  off.     At  the  same  time  that  the  compacting 
is  done  the  soil  should  be  pulverized,  thus  making  a  better  seed  bed 
for  the  crop. 

6.  Planting  the  Seed. — While  there  is  not  much  of  what  we 
usually  call  tillage  in  the  ordinary  seeding  of  crops,  yet  all  seeding 
is  accompanied  by  more  or  less  working  of  the  soil. 


TILLAGE  327 

IMPLEMENTS  OF  TILLAGE 

Tillage  implements  are  divided  into  five  classes — plows,  har- 
rows, compacters,  seeders,  and  cultivators. 

1.  Plows. — The.  mold-hoard  plow  is  one  of  the  most  common 
as  well  as  one  of  the  hest  implements  for  loosening  the  soil  and 


A  B  c 

FlO.    137. — Diagram  showing  the  theoretical  action  of  the  plow.     The  sliding  or  shearing  it; 
accompanied  by  more  or  less  of  a  rolling  action,  all  of  which  pulverizes  the  soil.     (King.) 

turning  under  vegetable  material..  It  brings  about  almost  a  com- 
plete inversion  of  the  furrow-slice,  and  in  doing  this  pulverizes  the 
soil.  The  mold-board  is  of  such  a  curvature  that  when  the  soil 
passes  over  it,  it  produces  a  shearing  force  in  the  soil  as  if  made  up 
of  different  layers  somewhat  similar  to  the  effect  of  bending  several 
leaves  of  a  book  and  brings  about  pulverization  (Fig.  137)  if  the 


A  n  c 

Fio.   138. — Showing  the  three  types  of  mold-hoards.    A-Sod.     B-General  purpose. 

C-Stubblc. 

soil  is  in  good  condition  for  plowing.  If  too  dry  so  that  the  soil 
is  cloddy  little  pulverization  is  accomplished.  If  the  soil  is  too  wet 
for  plowing  this  shearing  breaks  down  the  granules,  producing  par- 
tial puddling,  very  injurious  to  the  soil.  The  plow  should  be  set 
so  that  the  furrow-slice  will  be  cut  free  from  the  soil  beneath  and 
practically  all  inverted.  Mold-board  plows  are  divided  into  stubble, 
general  purpose,  and  sod  plows. 


328  SOIL  PHYSICS  AND  MANAGEMENT 

The  stubble  plow  (Fig.  138C)  has  a  short,  strongly  curved 
mold-board  and  is  probably  the  best  form  to  use  in  old  land.  In 
general  the  more  curvature  or  twist  there  is  to  the  mold-board  the 
greater  the  pulverization,  the  better  is  the  condition  of  the  soil  after 
plowing,  provided  it  has  the  proper  moisture  content.  This  plow 
is  not  desirable  to  use  in  breaking  sod,  because  of  the  rough  con- 
dition in  which  it  leaves  the  surface.  The  jointer  is  sometimes  used 


Fio.   139. — Plow  with  separate  jointer  and  rolling  coulter  attached  ready  for  use.     (Moline 

Plow  Company.) 

in  the  plowing  of  light  sods,  as  it  materially  aids  in  turning  under 
and  preventing  the  further  growth  of  grass  (Figs.  139  and  140). 

The  general  purpose  plow  (Fig.  138B)  is  a  form  intermediate 
between  the  stubble  and  sod  plows  in  length  and  curvature  of  mold- 
board.  It  may  be  used  for  either  stubble  or  sod.  It  does  not  pul- 
verize the  soil  so  thoroughly  as  the  stubble  mold-board,  and  as  a  con- 
sequence it  leaves  sod  in  much  better  condition  for  working  into 
a  good  seed  bed.  For  all  uses  it  is  probably  the  best. 


TILLAGE 


329 


Sod  plows  (Fig.  138A)  have  long,  slightly  curving  mold-hoards 
that  do  the  minimum  amount  of  pulverization  in  turning  the  fur- 
row-slice. They  are  used  principally  in 
the  plowing  of  tough  grass  sods,  since 
they  turn  the  furrow-slice  without 
breaking  it  very  much,  thus  leaving  a 
comparatively  smooth  plowed  surface. 
This  has  some  advantages  in  the  pro- 
duction of  a  seed  bed, 

A  form  of  the  mold-board  plow 
known  as  the  hillside  or  swivel  plow 
may  be  reversed  so  that  the  soil  may 
all  be  thrown  in  one  direction. 

The  disk  plow  (Fig.  141)  may  be 
used  under  some  conditions  to  good 
advantage.  If  the  soil  is  quite  com- 

pact  and  dry  it  may  be  used  where  it          faF-aS      *(£?]£ 
would    not   be   possible    for   the   mold-  Company.) 
board  to  do  any  work  at  all.     It  has  this  other  advantage,  that  it 
does  not  tend  to  produce  a  plowpan,  because  the  furrow-slice  is 


FIO.  140.—  TH.-  rombim-d  jointer 


Flo.   141. — Disk  plow.      (Molinr  Plow  Company.) 

broken  off  rather  than  cut  off.  Under  some  conditions  it  turns 
rubbish  under  better.  Disk  plows  are  extensively  used  in  arid  and 
semi-arid  regions,  but  may  be  used  successfully  on  almost  any  soil. 


330 


SOIL  PHYSICS  AND  MANAGEMENT 


FIG.   142. — Lister  for  preparing  the  ground  and  planting  corn.     Used  chiefly  in  the  semi- 
arid  regions.      (Moline  Plow  Company.) 

A  reversible  disk  for  hillside  plowing  has  some  advantages  over  the 
ordinary  reversible  mold-board  plow. 

A  deep  tilling,  double  disk  plow  for  stirring  the  ground  to  a 
depth  of  16  to  18  inches  is  used  in  some  sections.  This  does  noi, 
however,  bury  the  surface  soil  to  so  great  a  depth  as  would  be  indi- 
cated, but  mixes  this  deeper  soil  with  the  surface  to  a  greater  or  less 
extent.  The  disk  plow  cannot  be  used  in  stony  land  successfully, 
particularly  where  the  stones  are  firmly  set  in  the  soil. 

The  lister  (Fig.  142)  is  a  plow  used  particularly  in  semi-arid 
regions  for  the  preparation  of  the  ground  for  corn  planting,  and 
even  for  other  crops.  It  is  a  double  mold-board  plow,  and  when 
used  opens  a  furrow  in  which  the  corn  is  planted.  It  ridges  the 
land  and  gives  the  soil  an  excellent  chance  to  weather  (Fig.  143). 

The  subsoil  plow  (Fig.  144)  is  used  to  loosen  the  soil  in  the 
bottom  of  a  furrow  made  by  the  ordinary  plow.  It  consists  of  a 
shoe  which  merely  raises  the  soil,  but  does  not  throw  it  out. 


TILLAGE 


331 


Fio.   143. — Work  done  by  lister.      (Kansas  Station  )  ' 


Fio.   HI.— S 


2.  Harrows. — The  spike-tooth  harrow  is  the  form  commonly 
used  and  is  very  ell'ective  in  pulverizing  and  slightly  compacting 
freshly  plowed  land.  In  some  places  the  "A  "  harrow,  with  square 
teeth,  is  still  extensively  used,  and  is  especially  desiralile  in  stumpy 
land.  The  lever  harrow  (  Ki«r.  1  1">)  of  two  to  four  sections  is  very 
commonly  used,  sometimes  with  a  riding  attachment.  The  levers 
permit  the  slanting  of  the  teeth  so  that  any  ruhhish  will  easily  pass 
out  of  the  harrow. 


332 


SOIL  PHYSICS  AND  MANAGEMENT 


FIG.   145. — Spike-tooth  harrow 


Fia.   146. — Spring-tooth  harrow. 


The  spring-tooth  harrow  (Fig.  146)  is  used  quite  extensively 
in  regions  where  the  soil  is  in  rather  poor  physical  condition  and 
where  it  is  necessary  to  cultivate  as  well  as  harrow.  After  a  rain 


TILLAGE 


333 


this  harrow  will  do  more  efficient  work  in  loosening  the  soil  than 
the  ordinary  spike-tooth  harrow,  and  for  that  reason  is  used  mostly 

'1 


Fio.    US.— The  solid  disk. 


on  soils  that  are  deficient  in  organic  matter.     It  is  a  verv  good  imple- 
ment to  use  in  the  cultivation  of  alfalfa. 

The  Acme  or  blade  harrow  (  Fiir.  1  I?)  is  used  to  some  extent. 
and   is  an  excellent   implement  to  pulvcri/e  and  compact  the  soil. 


334 


SOIL  PHYSICS  AND  MANAGEMENT. 


The  bar  in  front,  if  properly  adjusted,  crushes  clods,  whife  the 
twisted  blades  stir  the  soil  and  destroy  any  weeds  that  may  have 
started.  For  this  purpose  it  is  better  than  the  spike-tooth  harrow. 


ia.   149. — The-cut  away  disk. 


Fia.   150. — The  spading  disk  harrow. 

The  disk  harrow  (Figs.  148,  149  and  150)  is  made  in  three 
forms — the  solid  disk,  the  cut-away,  and  the  spading  disk.  The  first 
two  act  somewhat  the  same  as  the  disk  plow,  hut  do  not  turn  the 
dirt  so  thoroughly,  yet  are  very  effective  in  stirring  the  soil.  The 


TILLAGE 


335 


degree  of  effectiveness,  however,  may  be  increased  or  diminished  bv 
adjusting  the  angle  of  the  disk  with  the  direction  of  movement. 
Next  to  the  plow  the  disk  is  one  of  the  most  important  and  useful 
implements.  It  may  he  used  very  effectively  before  the  plowing  is 
done,  and  is  one  of  the  host  tools  for  the  preparation  of  a  seed  bed. 
Either  the  solid  disk  or  the  cut-away  may  be  used  to  excellent 
advantage  in  cutting  up  corn-stalks  and  other  vegetable  material 
and  mixing  them  with  the  soil  before  plowing.  This  insures  the 
close  contact  of  the  furrow-slice  with  the  soil  beneath.  A  small 
rotary  spading  harrow  is  sometimes  attached  to  the  plow. 


I  in.    1")1. — Smooth  or  drum  roll(»r. 

3.  Compacters. — Compacting  is  necessary  because  most  of  out- 
crops require  a  firm  but  mellow  seed  bed.  In  manv  cases  in  our 
heavier  soils  clods  are  formed  which  require  the  use  of  the  roller 
to  crush,  while  in  the  case  of  sands,  sandy  loams,  and  many  silt, 
loams  the  soils  are  so  loose  that  root  development  and  moisture 
retention  are  interfered  with.  In  arid  and  semi-arid  regions  the 
subsurface  compacter  is  used  to  prevent  the  excessive  loss  of  moist- 
ure through  any  large  air  spaces  that  may  exist  in  the  soil.  The 
packing  also  increases  upward  capillary  movement  of  soil  moisture. 
and  consequently  less  water  is  lost  by  the  downward  movement. 

The  smooth  or  drum  roller  (Fig.   1-">1)   is  used  quite  exten- 


336 


SOIL  PHYSICS  AND  MANAGEMENT 


sively,  but  is  not  as  effective  as  some  other  forms  and  is  gradually 
being  replaced.  When  used  for  crushing  clods  these  are  frequently 
pressed  into  the  soil  without  being  affected  to  any  extent,  and  a 
subsequent  harrowing  before  a  rain  usually  brings  them  to  the  sur- 
face again.  Its  use  greatly  increases  evaporation  of  moisture. 


FIQ. 


Iti-packer,  a  form  of  corrugated  roller,  showing  the  work  done. 


iflil'A  '1   J|B 

fc^M&t  ' 

•*^ " 


Fio.   153. — Disk  drill  and  its  work. 


Corrugated  Roller. — The  smooth  form  of  roller  is  gradually 
being  displaced  in  the  corn  belt  by  the  culti-packer  or  corrugated 
roller  (Fig.  152),  which  consists  of  a  series  of  wheels  with  a  sharp 
ridge  about  two  to  two  and  one-half  inches  in  height.  This  imple- 
ment is  much  more  effective  in  crushing  clods  and  leaves  the  ground 
covered  with  a  thin  mulch. 


TILLAGE  337 

The  bar  roller  is  another  form,  made  up  of  a  series  of  bars 
running  lengthwise  of  the  roller.  'Phis  implement  is  better  than 
the  ordinary  drum  roller,  but  is  not  as  effective  as  the  corrugated 
roller  or  culti-packer. 

Flankers  made  by  bolting  together  two  or  three  two-inch 
boards  so  that  they  lap  about  half  may  be  used  to  good  advantage 
for  crushing  clods  and  levelling  without  compacting  to  any  extent. 

The  Campbell  subsurface  packer  (Fig.  107,  page  247)  is 
used  in  arid  and  semi-arid  regions.  Its  special  advantage  is  that 
it  compacts  deep,  freshly  plowed  soil,  leaving  a  mulch  on  the  sur- 
face. It  consists  of  a  number  of  wheels  with  a  wedge-shaped  edge. 
These  are  about  five  inches  apart  and  revolve  independently  of  each 
other.  As  this  wheel  presses  in,  the  soil  is  pushed  to  both  sides. 


Fin.   154.— Press  drill 


thus  closing  the  air  spaces,  leaving  a  loose  mulch  on  the  surface. 
This  may  be  used  in  sandy  soils  in  humid  regions  to  very  good 
advantage. 

4.  Seeders  (Figs.  153,  154,  155).— The  tillage  done  by  seeders 
is  purely  incidental,  yet  in  many  cases  very  essential.      Drills  almost 
invariably  till  the  soil  to  a  considerable  extent  in  opening  a  furrow 
every  six  to  eight  inches  in  which  to  deposit  the  seed.     Where  press 
drills  are  used  the  soil  is  compacted  upon  the  seed.     In  the  planting 
of  corn  with  the  ordinary  planter  the  tillage  is  similar  to  that  of  the 
press  drill,  hut  not  so  extensive.      Many  broadcast    seeders,   bow- 
ever,  accomplish  no  cultivation. 

5.  Cultivators. — Cultivators   are    for   use   in    intertilled   crops. 
Some  stir  the  soil  to  a  depth  of  one  inch  or  less,  while  others  work 


338 


SOIL  PHYSICS  AND  MANAGEMENT 


to  a  depth  of  four  inches  or  more.    They  may  he  divided  into  shovel, 
disk,  blade  cultivators,  and  wceders. 


Fio.   155. — Ordinary  corn  planter  with  attachment  for  planting  cowpeas  in  hill  or  row  with 

corn. 


Fio.   150. — Three-shovel  cultivator. 


The  shovel  cultivators  (Fig.  156)  vary  in  the  number  and  size 
of  the  shovels  used.  There  may  be  two  large  sliovels  on  each  gang, 
three  medium,  or  four  small  ones.  The  depth  to  which  they  go 
varies  directly  with  the  size  of  the  shovels.  It  is  not  unusual  to 


ULLAGE 


339 


see  cultivation  done  over  four  inches  deep  with  the  large  or  medium 
shovel.  There  are  two  types  of  cultivators  with  four  or  five  small 
shovels  in  each  gang — the  eagle  claw  and  the  spring-tooth.  These 
penetrate  the  soil  to  a  depth  slightly  more  than  two  inches.  A  form 
of  the  shovel  plow  is  made  hy  replacing  the  inside  shovel  with  a 
little  diamond  or  har  share  plow  hy  which  the  soil  is  thrown  up 
into  a  high  ridge  along  the  corn  TOW. 

The  disk  cultivators  (Fig.  157)  consist  of  three  disks  on  each 
side  and  may  he  used  to  good  advantage  where  the  hind  weed  or 
wild  morning  glory  abounds.  As  these  cultivators  are  commonly 
used  the  disks  are  set  to  run  deep  aud  corn-row  ridges  result.  They 


Fia.   157. — Disk  cultivator. 


Fia.    158. — Surface  or  blade  cultivator 
with  levoler. 


may,  however,  he  adjusted  to  run  shallow  and  leave  the  soil  com- 
paratively level. 

Blade  cultivators  (Fig.  1  •">!•>)  consist  of  four  hlades,  two  to 
each  gang,  from  11  to  IS  inches  long  and  two  to  three  inches  wide. 
These  are  placed  at  an  angle  such  that  there  is  a  slight  tendency 
to  move  some  soil  toward  the  row,  hut-  most  of  it  falls  over  the  hlade, 
leaving  a  loose  mulch.  This  implement  is  very  satisfactory  for 
shallow  cultivation,  and  may  he  so  adjusted  as  to  stir  the  soil  to  a 
depth  of  three  inches  or  more.  Cultivation  to  this  depth,  however, 
is  seldom  advisahle  hecause  of  the  injury  to  the  roots.  The  hlades 
cover  the  entire  space  hetwcen  the  rows,  so  there  is  very  little  chance 
for  weeds  to  escape.  "  A  "-shaped  hlades  are  heing  used  to  some 
extent.  The  sweep  is  a  modification  of  the  hlade  cultivator.  Kach  of 
the  ahove  is  made  in  hoth  one-  and  two-row  forms.  Various  imple- 
ments for  use  with  one  horse  are  found,  such  as  the  double-shovel, 
the  five-shovel,  and  fourteen-tooth  cultivators. 


340 


SOIL  PHYSICS  AND  MANAGEMENT- 


The  weeder  (Fig.  159)  consists  of  a  large  number  of  narrow 
spring  teeth  well  adapted  for  shallow  cultivation  of  such  crops  as 
corn,  cowpeas  and  beans  in  humid  sections  and  for  most  of  the 
crops  in  semi-arid  regions.  For  this  implement  to  do  its  best  work 


Fia.  159.  —Weeder. 


the  soil  should  be  mellow  and  in  good  tilth  and  the  weeds  small, 
but  if  the  soil  is  compact  or  the  weeds  quite  large  it  is  of  little  value. 


PLOWING 


Plowing  is  an  art.     It  is  one  of  the  most  important  as  well  as 
the  most  common  methods  of  preparing  the  soil  for  the  crop.    From 


Fio.  160. — An  early  form  of  plow. 

the  beginning  of  agriculture-  some  form  of  plow  has  been  in  use. 
Even  at  the  present  time  in  some  countries  the  plow  is  a  very  primi- 
tive implement,  as  shown  in  Fig.  160,  and  does  very  inefficient  work. 
In  North  America  we  find  the  two  extremes.  In  parts  of  Mexico 
the  people  are  still  using  the  most  primitive  form  of  plows.  In  the 


TILLAGE 


341 


wheat  region  of  the  northwest  the  powerful  tractor,  with  its  six  to 
ten  plows  and  accompanying  disks  and  harrows,  may  be  seen  pre- 
paring the  soil  for  the  crop.  These  improvements  have  materially 
reduced  the  cost  of  raising  a  bushel  of  wheat.  In  the  southern  part 
of  the  United  States  many  one-horse  plows  are  used.  Plowing, 
when  well  done,  accomplishes  more  of  the  objects  desired  in  tillage 
than  any  other  operation.  The  plowing  done  by  the  crude  imple- 
ments of  primitive  peoples  falls  far  short  of  good  results.  It  enables 
them,  however,  to  put  their  soil  in  somewhat  better  condition,  and 
without  doubt  they  grow  larger  crops  than  without  even  this  simple 
operation. 


Fio.   Ifil.— Tin 


(1  represents  Rood  work. 


Good  plowing  saves  labor  in  Hie  preparation  of  a  seed  bed.  It 
gives  all  plants  of  the  crop  an  equal  chance  and  all  a  much  greater 
advantage  than  on  poor  plowing.  For  good  plowing  the  following 
things  are  essential : 

1.  The  entire  furrow-slice  should  be  cut  loose  from  the  soil 
beneath  and  all  turned.  In  other  words,  u cutting  and  covering" 
is  not  good  plowing. 

^.  The  plowing  should  be  done  to  a  certain  depth  to  produce 
pulverization.  In  most  cases  the  soil  is  n<>t  pulveri/ed  to  any  extent 
when  the  furrow-slice  is  only  three  or  four  inches  thick.  For  best 
pulverization  plowing  should  lie  done  live  to  seven  indies  deep. 


342 


SOIL  PHYSICS  AND  MANAGEMENT 


3.  The  turning  under  of  rubbish  is  essential  to  good  plowing. 
To  do  this  properly  the  furrow-slice  must  be  five  or  six  inches  thick, 
and  in  some  cases  chains  or  weed  hooks  are  necessary. 

4.  The  furrow  should  be  kept  straight  or  at  least  parallel  with 
the  middle   ridge,   as   a   crooked   furrow   almost  always   indicates 
"  cutting  and  covering  "  at  some  points. 

1.  Time  of  Plowing. — The  time  when  plowing  should  be  done 
varies  with  climatic,  crop,  and  soil  conditions.     In  semi-arid  regions 


••••HE*  >*  '         ^5<aEHBi^^BBKHHHm 

FlO.   162. — Good  plowing  in  stubble  land.     (.lanesville  Machine  Company.) 


Fia.   163. — A  crooked  furrow  docs  not  look  well,  even  if  the  plowing  is  good. 


TILLAGE  343 

plowing  should  follow  the  preceding  crop  as  soon  as  possible.  The 
primary  object  to  be  accomplished  is  conservation  of  moisture.  In 
humid  regions  the  time  of  plowing  depends  upon  the  crop  to  some 
extent:  The  plowing  for  wheat  and  rye  must  he  done  in  summer, 
while  for  corn,  cotton,  oats,  barley,  cowpeas,  and  soybeans  it  may 
he  done  either  in  fall  or  spring. 

(a)  Fall  Plowing. — If  the  plowing  is  done  in  the  fall  the 
ground  should  be  plowed  as  late  as  possible  unless  a  catch  crop  is 
planted  to  conserve  the  available  nitrates.  When  the  ground  is 
stirred  by  the  plow  it  produces  conditions  very  favorable  for  nitrifi- 
cation, which  takes  place  at  the  expense  of  the  organic  matter  in  the 
soil,  resulting  in  the  production  of  soluble  plant  food  that  may  be 
leached  out  of  the  soil  during  the  winter  and  spring.  If  a  catch 
crop  is  grown  the  plants  take  up  the  soluble  plant  food  and  preserve 
it.  In  the  case  of  very  late  fall  plowing  the  conditions  are  usually 
not  favorable  for  any  large  amount  of  nitrification,  and  the  result  is 
that  little  soluble  plant  food  will  be  formed  before  winter. 

The  soil  never  becomes  too  dry  to  be  plowed  in  the  fall  when 
looked  at  from  the  standpoint  of  benefit  to  the  soil.  It  may  become 
so  dry,  however,  that  it  will  be  impossible  from  a  power  standpoint 
to  do  the  work  with  horses.  The  tractor  may  be  used  to  good  advan- 
tage under  these  conditions. 

There  are  several  important  advantages  in  fall  plowing:  first,  the 
work  may  be  done  at  the  time  of  the  year  when  other  work  is  less 
pressing;  second,  the  organic  matter  turned  under  during  the  fall 
has  sufficient  time  to  partly  decay  before  the  crop  is  put  in,  thus 
liberating  the  plant  food  and  giving  the  soil  time  to  settle  and  re- 
establish capillary  connection;  third,  many  insects  and  their  eggs 
are  destroyed  by  disturbing  them  late  in  the  fall,  which  is  especially 
true  of  the  ant  hills  containing  the  eggs  of  the  corn  root  aphis; 
fourth,  the  improvement  of  the  tilth  of  the  soil  by  exposing  it  to 
freezing  and  thawing  and  wetting  and  drying  during  winter  and 
spring,  producing  a  granular  condition  that  is  very  desirable.  This 
is  especially  true  of  heavy  soils  containing  a  fair  supply  of  organic 
matter. 

As  a  general  rule,  soils  deficient  in  organic  matter  do  not  re- 
ceive as  much  benefit  from  fall  plowing  as  soils  well  supplied  with 
this  constituent.  1 1' deficient  in  organic  matter,  free/ing  and  thaw- 
ing cause  the  soil  to  run  together  instead  of  producing  granula- 
tion. Timber  soils  generally  are  not  as  well  adapted  to  fall  plow- 


344  SOIL  PHYSICS  AND  MANAGEMENT 

ing  as  prairie  soils  because  of  the  lack  of  organic  matter.  Even 
the  lighter  colored  phase  of  brown  silt  loam  packs  badly  during 
winter.  If  fall  plowed,  sandy  loams  are  liable  to  be  damaged  by 
blowing.  Heavy  soils  are  especially  benefited  by  fall  plowing. 

(b)  Spring  Plowing. — A  very  large  amount  of  plowing  must 
necessarily  be  done  in  the  spring  because  the  crop  of  the  preceding 
year  was  not  taken  off  in  time  for  fall  plowing.  It  is  very  essential 
that  some  preparatory  work  be  done  previous  to  the  plowing.  This 
should  usually  consist  of  thoroughly  disking  (Fig.  164)  the  ground 
to  cut  up  the  vegetable  material  and  mix  it  with  the  soil  so  that, 
when  the  furrow-slice  is  turned  and  compacted  slightly,  close  capil- 
lary connection  may  be  established  at  once.  Where  corn-stalks  are 
to  be  turned  under,  as  is  frequently  done  in  the  corn  belt,  the  cutting 


^          .-"£? 

••'    r      "•':*•.>•*"• 


Fia.   164. — Previous  to  plowing,  disking  should  be  done  to  cut  up  the  corn-stalks  or  other 
vegetable  matter  and  produce  a  deep  mulch. 

up  of  the  stalks  by  the  disk  is  a  very  important  process,  since  when 
plowed  the  fine  soil  filters  in  around  the  stalks  and  does  not  permit 
the  formation  of  large  air  spaces  that  aid  in  drying  the  soil.  This 
disking  will  also  prevent  evaporation,  so  that  if  plowed  later  it  will 
be  comparatively  free  from  clods. 

2.  Depth  of  Plowing. — Poor  and  badly-worn  soils  should  be 
plowed  deeper  than  rich,  productive  ones.  Our  cereals  and  grasses 
are  shallow  rooting  plants,  the  major  part  of  the  roots  developing 
in  the  plowed  soil.  This  forms  their  natural  and  most  accessible 
feeding  area.  Within  certain  limits  the  deeper  the  plowing  the 
better  the  chance  of  the  crop  for  getting  an  abundance  of  food. 
If  the  plowing  is  done  too  deep  the  surface  soil  with  its  swarms 
of  bacteria  will  be  buried  below  the  zone  of  most  favorable  action 
and  a  smaller  amount  of  available  food  will  be  developed  for  the 


TILLAGE  345 

crop.  Experience  indicates  that  eight  or  nine  inches  is  about 
the  limit.  For  rich,  deep  soils  six  to  seven  inches  is  sufficient.  This 
gives  a  deep  reservoir  for  water  storage  and  an  abundance  of  soil 
for  root  development. 

Deep  Tilling. — Deep  tilling  plows  have  been  put  on  the  market, 
by  which  plowing  may  be  done  to  a  depth  of  twelve  to  eighteen 
inches.  As  a  result  of  nine  tests  for  corn,  the  yield  was  2.7  bushels 
higher  for  ordinary  plowing  than  where  plowed  twelve  to  fourteen 
inches  deep.  This  may  have  some  advantages  for  alfalfa  and  other 
deep-rooting  crops.  The  Kentucky  Station  found  an  increase  of 
416  pounds  of  alfalfa  hay  in  two  cuttings  in  favor  of  deep  tilling. 

Subsoiling. — Subsoil  plows  have  been  used  for  loosening  the 
soil  to  a  greater  depth  than  is  possible  with  the  ordinary  plow.  This 
practice  was  more  common  a  few  years  ago  than  at  present.  The 
results  do  not  indicate  that  the  operation  in  humid  soils  is  of  very 
much  value.  As  a  result  of  40  tests  in  southern  Illinois  the  sub- 
soiled  land  gave  an  average  of  2.7  bushels  less  than  the  land  not  sub- 
soiled.1  This  practice  may  have  some  value  in  semi-arid  regions  and 
for  certain  crops,  but  it  is  certain  that  it  has  very  little  value  for 
the  principal  cereal  crops  in  humid  regions. 

Dynamiting. — The  use  of  dynamite  for  breaking  up  the  im- 
pervious  or  hardpan  subsoils  has  been  resorted  to  in  some  cases. 
This  is  a  good  practice  where  trees  are  to  be  planted.  A  charge  of 
dynamite  is  exploded  and  the  tree  is  planted  in  the  loose  soil  thus 
produced.  The  expense  involved  in  breaking  up  the  subsoil  in  this 
way  makes  the  practice  almost  prohibitive  for  ordinary  crops,  unless 
the  increase  in  yield  is  much  greater  than  the  experiments  up  to 
the  present  would  indicate. 

Effect  of  Deep-Rooting  Crops. — Without  much  doubt  nature 
has  provided  the  best  method  of  deep  tillage.  This  is  by  means  of 
deep-rooting  plants,  and  more  especially  legumes.  A  crop  of  red, 
mammoth,  sweet  clover  or  alfalfa  fills  the  soil  with  roots  and  leaves 
it  open  and  readily  permeable  to  water  and  air.  These  roots  extend 
to  a  depth  of  several  feet  and  render  heavy  clays  pervious,  bring 
plant  food  from  the  subsoil  to  the  surface,  and  benefit  such  soils  in 
.various  other  ways.  The  crop  should  be  seeded  much  thicker  than  is 
done  ordinarily.  There  should  be  from  six  to  twelve  or  more  plants 
to  the  square  foot,  as  one  plant  to  the  square  foot  is  of  comparatively 
little  benefit. 

Preparation  of  the  Seed  Bed. — The  ordinary  farm  crops  re- 
quire better  conditions  for  their  growth  than  the  wild  plant*  with 


346 


SOIL  PHYSICS  AND  MANAGEMENT 


which  we  are  familiar.  The  soil  in  which  they  grow  must  be  suf- 
ficiently loose  so  the  roots  have  little  difficulty  in  penetrating  it. 
The  growth  they  make  depends  to  a  large  extent  on  the  area  over 
which  the  roots  spread.  Hence  the  necessity  of  producing  a  deep, 
mellow  seed  bed  that  will  allow  free  root  development. 

Clods  are  of  no  value  in  a  field,  but  are  always  a  source  of  annoy- 
ance. They  are  generally  the  products  of  shiftless  and  unscientific 
methods  of  farming  rather  than  of  some  inherent  fault  or  bad 
quality  of  the  soil.  Soils  if  worked  at  the  proper  time  and  after 
proper  preparation  respond  to  good  tillage.  The  disk  is  one  of  the 
best  implements  for  preventing  the  formation  of  clods  and,  to- 
gether with  the  culti-packer,  for  destroying  them  if  they  once  form. 


Fro.  165. — Grain  produced  from  five  tenth-acre  plots  prepared  in  different  ways  lor  winter 
wheat.     (L.  E.  Call.)     Kansas  Station. 

Clods  are  of  no  use  to  a  growing  crop,  but  on  the  contrary  lock 
up  large  quantities  of  food  and  become  prisons  for  millions  of  bac- 
teria that  would  otherwise  be  working  for  the  farmer.  Fields  are 
sometimes  seen  in  which  at  least  one-third  of  the  plant  food  of  tbe 
plowed  soil  is  locked  up  in  clods.  Even  if  the  clods  are  turned 
under  and  covered  by  mellow,  moist  soil,  weeks  are  required  before 
they  become  thoroughly  moistened  unless  rain  falls. 

1.  Wheat. — Plowing  for  wheat  should  be  done  as  soon  as  pos- 
sible after  the  removal  of  the  preceding  crop  and  from  five  to  seven 


TILLAGE 


347 


inches  deep.  If  the  ground  is  dry  or  liable  to  become  dry  before 
plowing  can  be  done  clods  may  be  prevented  from  forming  by 
thorough  disking.  This  kills  weeds  and  produces  a  mulch  which 
conserves  moisture  and  later  plowing  may  be  done  very  satisfactorily 
without  any  great  amount  of  clods.  The  impression  prevails  that 
since  wheat  is  a  very  shallow  rooting  plant  the  plowing  should  be 
done  somewhat  shallow,  but  experiments  show  that  a  depth  of  seven 
inches  is  not  too  deep  (Fig.  !<>•>).  Immediately  after  the  plowing 
is  done  it  is  necessary  to  work  the  soil  by  means  of  a  disk  and  harrow 

Mdhoih  of  Preparing  Land  for  Wheat  -  (Continuous  Wheat) 


Method  of  preparation 

Average  of  3  years,  1!H  1  -HUH 

Yield  per 
ncre,  bushels 

Cost  per  arre 
for  preparation 

Value  of  orop 
les.s  cost  of 
preparation* 

Disked,  not  plowed   

6.(>3 
13.24 
14.15 

22.19 
20.48 
20.77 
27.11 
19.71 
23  40 

$2.07 

2.x:} 
3.33 

4.00 
3.33 
4.85 
5.35 
3.93 
4.93 
3.92 
4.05 

$3.64 

S.35 
8.60 

1G.34 
13.65 
12.25 
10.87 
12.37 
14.30 
14.73 
14.53 

Plowed,  Sept.  15,  3  inches  deep  
Plowed,  Sept.  15,  7  inches  deep  
Plowed,     Aug.    15.    7    inches    deep 
(worked)  

Plowed,  Aug.  15;  7  inches  deep,  not 
worked  till  Sept.  15  

Plowed,  July  15,  -3  inches  deep 
(worked)  '.  

Plowed,  July  15,  7  inches  deep 
(worked)  

Double  disked  July  15,  plowed 
Sept.  15  

Double  disked  July  1  5,  plowed  Aup.  1  5 
7  inches  deep 

Listed  July  15,  5  inches  deep,  ridges 
split  Aug.  15  . 

22.  90 
22.77 

Listed  July  15.  5  inches  deep;  worked 
down  

*  Wheat  market  value  when  threshed. 

to  conserve  moisture,  develop  plant  food,  and,  most  important  of 
all,  prevent  the  growth  of  weeds.  The  seed  bed  for  wheat  must  be 
firm.  If  the  soil  is  very  open  at  seeding  time  tin-  free/ing  in  winter 
will  have  a  greater  tendency  to  heave  the  soil  and  kill  the  wheat, 
especially  if  the  land  is  not  well  drained.  The  roller  or  culti- 
packer  can  be  used  to  excellent  advantage  in  the  preparation  of  the 
seed  bed  for  this  crop. 

In  seeding  wheat  in  corn  ground  after  the  corn  has  been  taken 
off  the  field  for  the  silo,  or  placed  in  the  shock,  a  sufficiently  good 
seed  bed  may  he  produced  with  the  disk.  The  settling  of  the  soil 


348  SOIL  PHYSICS  AND  MANAGEMENT 

during  the  summer  will  make  it  sufficiently  compact  and  a  thin 
stratum  of  two  to  four  inches  in  depth  mellowed  somewhat  by  the 
disk  will  provide  an  excellent  seed  bed.  Wheat  is  sometimes  seeded 
in  the  standing  corn  and  in  such  case  no  preparation  is  necessary. 
The  crop  is  handicapped,  however,  because  the  corn  has  left  the 
soil  in  poor  condition  in  regard  to  moisture  and  plant  food. 

The  preceding  table  shows  that  deep,  early  plowing  with  working 
till  seeding  time  has  given  the  greatest  profit. 

The  soil  for  wheat  should  be  well  drained.  This  is  very  essential, 
especially  in  temperate  regions  where  freezing  and  thawing  occur. 
The  great  objection  to  growing  wheat  formerly  was  the  winter  killing 
caused  by  a  poorly  drained  seed  bed. 

2.  Corn. — The  plowing  for  corn  may  be  done  either  in  fall  or 
spring  and  the  production  of  the  seed  bed  is  somewhat  different  in 


Fro.   166. — A  Rood  seed  bed  on  stalk  ground. 

the  two  cases.  With  fall  plowing  the  ground  should  be  disked  or 
worked  in  some  way  as  early  as  possible  in  the  spring  to  a  depth  of 
three  to  five  inches.  This  conserves  moisture,  raises  the  temperature 
of  the  soil  and  destroys  any  weeds  that  may  have  started.  This 
disking  should  be  continued  at  intervals  of  ten  days  or  two  weeks 
until  the  time  for  planting.  The  object  is  to  destroy  as  many 
weeds  as  possible  before  the  crop  is  planted,  as  cultivation  for  this 
purpose  is  much  more  effective  at  this  time.  The  disking  should 
be  done  deep  to  thoroughly  aerate  the  soil  and  encourage  the  develop- 
ment of  plant  food.  Corn  on  fall-plowed  land  is  said  by  some 
farmers  to  "  fire  "  easily.  This  "  firing  "  may  be  due  to  two  causes : 
first,  to  lack  of  moisture,  and,  second,  to  lack  of  available  nitrates. 
Fall  plowing,  unless  the  soil  is  in  good  tilth,  tends  to  dry  out  early 


TILLAGE 

and  rapidly.  The  rains  have  compacted  it,  the  ground  is  hare,  and 
with  the  strong  winds  of  March  and  April  there  is  nothing  to  prevent 
rapid  loss  of  water.  Deep,  early  disking  in  the  preparation  of  the 
seed  bed  will  conserve  moisture  and  in  this  way  tend  to  eliminate 
this  danger  from  "firing."  Thorough  and  deep  disking  also  en- 
c<  urages  the  formation  of  large  quantities  of  available  nitrates.  Jn 
the  case  of  shallow  and  insufficient  disking  the  fall-plowed  land  is 
left  compact  and  somewhat  cloddy,  with  conditions  for  nitrification 
and  conservation  of  moisture  very  unfavorable.  Such  preparation 
has  a  tendency  to  encourage  "  firing/' 

The  preparation  of  the  seed  bed  from  spring-plowed  land  does 
not  require  so  much  working  during  the  average  season  as  for  fall- 
plowed  land.  The  ground  should  be  thoroughly  worked  with  disk 
or  harrow  immediately  after  plowing.  A  rotary  harrow  attached 
to  the  plow  does  good  work.  This  working  should  be  continued  at 
intervals  the  same  as  for  fall  plowing.  When  ready  to  plant,  the 
harrow  may  be  sufficient  to  put  the  soil  in  fine  condition  (  Fig.  1  (>(>). 
All  weeds  should  be  killed.  If  very  few  rains  occur  in  the  spring 
after  plowing  is  done  it  may  be  necessary  to  use  the  roller,  since 
corn,  like  wheat,  requires  a  firm  seed  bed  with  a  mellow  surface. 
Too  much  work  can  never  be  done  in  the  preparation  of  the  seed 
bed.  The  best  time  to  destroy  weeds  in  corn  is  before  the  crop  is 
planted.  The  cultivation  at  that  time  is  much  more  efficient  than 
at  any  time  thereafter. 

3.  Oats. — The  almost  universal  practice  in  the  corn  belt  is  to 
sow  oats  where  corn  grew  the  preceding  year.  It  was  an  early 
practice  in  some  regions  to  sow  the  oats  in  February  or  March 
without  preparing  any  seed  bed  whatever.  Sometimes  fairly  sat- 
isfactory results  were  obtained.  Hut  as  the  physical  condition  of 
the  soil  became  poorer  the  necessity  for  a  better  seed  bed  for  the 
oat  crop  has  become  more  imperative.  A  very  good  way  for  pre- 
paring the  ground  for  oats  is  to  plow  it  in  the  fall  and  then  disk 
thoroughly  in  the  spring.  In  the  corn  belt,  however,  the  apparent 
necessity  for  pasturing  the  corn-stalks  does  not  favor  this  prac- 
tice. Oats  do  not  require  a  deep  seed  bed,  but  it  should  be  well 
prepared.  The  common  practice  in  the  corn  belt  is  to  disk  the 
ground  from  one  to  three  times  and  give  it  a  final  harrowing. 
The  oats  may  be  seeded  at  any  time,  either  before  the  first  disking  or 
between  the  two  diskings.  F.ven  in  the  best  of  soils  one  disking  is 
not  sufficient,  although  this  is  not  an  uncommon  practice.  The 
stalks  to  a  certain  extent  prevent  the  full  efficiency  of  the  disk  and  in 


350  SOIL  PHYSICS  AND  MANAGEMENT 

inauy  cases  a  considerable  portion  of  the  oats  are  not  covered,  being 
in  some  cases  by  actual  count  one-eighth  of  the  amount  seeded. 

Plowing  the  ground  before  seeding  aids  in  producing  an  ex- 
cellent seed  bed;  however,  it  will  be  too  loose  unless  thoroughly 
firmed.  The  harrow  and  cornpacter  should  be  used,  and  if  the 
soil  is  well  supplied  with  organic  matter  so  it  will  not  bake  it 
should  be  rolled  after  the  seeding  is  done.  The  disk  drill  has  some 
advantage  over  the  broadcast  seeder  for  seeding  oats,  and  the  fact 
that  it  co'  3rs  practically  all  the  seed  is  a  decided  advantage.  Only 
about  two-thirds  as  much  seed  will  be  required  as  when  seeded 
broadcast. 

Cultivation. — Object. — The  objects  to  be  accomplished  in  the 
cultivation  of  a  crop  are:  first,  and  primarily,  the  killing  of 
weeds;  second,  the  conservation  of  moisture;  and,  third,  aeration. 
While  the  conservation  of  moisture  has  usually  been  placed  first, 
recent  experiments  show  that  cultivation  for  the  killing  of  weeds  in 
humid  regions  is  of  vastly  more  importance  to  the  crop  than  for 
the  conservation  of  moisture.  It  is  a  question  whether  this  may 
not  be  true  in  semi-arid  regions  as  well.  Weeds  require  both 
moisture  and  plant  food  for  their  growth  and  are  much  better  for- 
agers than  the  cultivated  crop.  At  the  Illinois  Station  (table,  page 
352),  as  a  result  of  nine  years'  investigation,  corn  with  weeds  de- 
stroyed by  a  hoe  without  producing  a  mulch  gave  a  yield  of  48.9 
bushels  per  acre  for  a  nine-year  a\rerage,  while  for  the  same  time 
corn  in  which  weeds  were  allowed  to  grow  produced  7.5  bushels  per 
acre,  or  41.4  bushels  in  favor  of  preventing  the  growth  of  weeds 
(Figs.  167,  168,  169).  In  order  to  determine  whether  it  was  the 
lack  of  the  plant  food  or  the  moisture  that  caused  the  greater  loss, 
part  of  each  plot  in  which  the  weeds  were  allowed  to  grow  was  sup- 
plied with  all  the  moisture  the  crop  and  weeds  needed,  and  as  a  five- 
3'ear  average  the  yield  was  increased  2.5  bushels  over  the  plots  where 
no  water  was  applied.  This  shows  rather  conclusively  that  the 
greatest  loss  was  caused  by  depriving  the  corn  of  food. 

Value  of  the  Mulch. — In  this  same  experiment  the  plots  men- 
tioned above  in  which  the  weeds  were  kept  down  with  a  hoe  with- 
out producing  a  mulch  gave  a  yield  of  48.9  bushels,  while  the  corre- 
sponding plots  which  were  cultivated  gave  a  yield  of  43.3  bushels,  or 
5.6  bushels  were  lost  due  to  damage  by  cultivation.  Moisture  de- 
terminations in  each  of  these  three  plots  were  made  and  it  was 
found  that  the  amount  of  moisture  in  the  uncultivated  plot  actually 
exceeded  that  of  the  cultivated  by  0.3  per  cent  for  an  eight-year 


TILLAGE 


351 


" 


FIG     107. — Nine-year  average  yield  43. 3  bushels  per  aero. 


ir,n     if,s  — Nino-vonr  avrrneo  yield  1S.«)  tuislicls  por  ncro 


Fia.   109. — Nino-y<>nr  nvoragp  yiold  7  1  bushels  per  acre. 


352 


SOIL  PHYSICS  AND  MANAGEMENT 


average.  It  is  without  doubt  true  that  if  the  ground  is  plowed  to  a 
depth  of  six  or  seven  inches,  and  a  good  seed  bed  produced,  there 
is  very  little  necessity  for  cultivation  of  corn  on  silt  loams  and 
sandy  loams  to  conserve  moisture.  It  will  be  seen  from  the  following 
table  that  during  the  dry  years  of  1911,  1913,  and  1914  the  yield  of 
corn  on  the  uncultivated  plots  was  5  to  10  bushels  more  than  on 
the  corresponding  cultivated  ones.  The  mulch  should  have  had  its 
greatest  effect  during  these  seasons  if  it  was  of  much  use  in  con- 
serving moisture  for  the  crop. 

Results  of  Cultivation  of  Corn  3 —  Each  is  an  Average  of  Two  Plots  (Bushels 

Per  Acre) 


Treatment 

1906 

1907 

1908 

1909 

1910 

1911 

1912 

1913 

1914 

1915 

64.9 
72  9 

9-year 
average 

Average* 
per  cent 
of  No.  5 

1.  Not  plowed  nor  cul- 
tivated,      weeds 
kept     down     by 
scraping  with  hoe 
2.  Plowed,    seed    bed 
prepared,  no  cul- 
tivation,     weeds 
kept     down     by 
scraping  with  hoe 
3.  Plowed,    seed    bed 
prepared,    weeds 
allowed  to  grow 
4.  Plowed,    seed    bed 
prepared,    weeds 
allowed  to  grow, 
irrigated 
5.  Plowed,    seed    bed 
prepared,     culti- 
vated 3  times 
0.   Plowed,    seed    bed 
prepared,     culti- 
vated   3    times, 
irrigated 
7.  Plowed,    seed    bed 
prepared,     culti- 
vated    3     times, 
irrigated,     fertil- 
ized 

38.3 
44  0 

25.0 
330 

28.6 
50.7 

33.1 
40  5 

25.5 
39.8 

46.1 
75  5 

16.5 
34  0 

38.5 
500 

35.2 
48.9 

81.3 

112.9 
17.1 

22.8 
100.0 

115.5 
158.4 

0.0 

16.0 

10.2 

.4 

.9 

2.6 
34  5 

7.9 

11.5 
65  ? 

10.4 

112.:; 
?i  q 

12.3 

20.4 

40  f> 

8.6 

5.9 

760 

7.4 

10.  5t 
43.4J 

44  7 

49.6 

?50 

31  4 

45  7 

46.2 
69.7 

49.S 
102.2 

28.2 

40.0 

50.3 
78.3 

55.0 
77.3 

61.2 
93.0 

41.2 
50.6 

56.2 
56.1 

70.4 
72.0 

50.  2J 
74.9s 

*  Based  on  all  comparable  yields, 
t  Five-year  average, 
j  Ten-year  average. 
8  Eight-year  average. 

The  cultivation  was  done  so  as  to  produce  a  mulch  from  2y2  to 
3y2  inches  in  depth.  (See  Figs.  170  and  171.)  During  the  years 
mentioned  the  mulch  was  so  dry  and  loose  that  the  roots  of  the 
corn  did  not  penetrate  it,  so  that  if  it  had  any  value  at  all  it  was  in 
conserving  moisture.  The  corn  roots  generally  develop  most  abun- 
dantly in  the  plowed  soil.  By  cultivating  three  inches  deep  the  crop 
was  enabled  to  use  only  one-half  of  the  plowed  soil,  and  there  was 
no  doubt  that  the  stirred  soil  was  worth  more  to  the  crop  for  the 


ULLAGE 


353 


plant  food  it  contained  than  for  the  moisture  it  conserved.  The 
experiment  was  conducted  on  the  brown  silt  loam,  the  common 
corn-belt  soil  of  Illinois.  The  same  experiment  was  tried  on 
the  gray  silt  loam  on  tight  clay  with  somewhat  similar  results,  as 
shown  in  this  table : 

Results  of  Cultivation  of  Corn  on  Gray  Silt  Loam  on  Tight  Clay  at  Fairfield, 
Wayne  County,4  Illinois  (Yields  in  Bushels  Per  Acre) 


Treatment 

1908 

1911 

1912 

1913 

1914 

3-year 
average 

5-year 
average 

Average 
percent 
of  No.  4* 

1.  Not   plowed,    not    culti- 

vated, weeds  kept  down 

by  scraping  with  hoe 

4.0 

3.2 

22.8 

0.0 

0 

10.0 

0.0 

31.4 

2.  Plowed,    seed    bed    pre- 

pared, weeds  kept  down 

by  scraping  with  hoe 

10.7 

22.1 

55.0 

0.0     0 

31.5 

18.9 

98.9 

3.  Plowed,    seed    bed    pre- 

pared,   weeds  allowed 

to  grow 

8.1 

8.7 

14.0     0.0     0        10.5 

0.3 

33.0 

4.  Plowed,    seed    bed    pre- 

pared,    cultivated     3 

times 

23.8 

24.0 

45.8 

2.1 

0 

31.2 

19.1 

100.0 

5.  Plowed,    seed    bed    pre- 

pared,    cultivated     3 

times,     manure,     rock 

phosphate,  limestone 

41.5 

32.6 

G2.1 

14.0 

0 

45.4 

30.2 

15S.1 

*  Computed  from  5-yenr  average. 

The  Department  of  Agriculture"  reports  a  number  of  experi- 
ments somewhat  similar  to  this,  and  the  average  yield  of  corn  on 
the  uncultivated  plots  was  52.0  bushels,  while  that  of  the  cultivated 
was  52.5  bushels  per  acre.  These  were  conducted  on  various  kinds 
of  soils  in  2S  different  states.  The  necessity  for  cultivation  is 
greater  on  heavy  soils  than  on  light  ones.  -This  is  shown  bv  the 
fact  that  uncultivated  sandy  loams  and  sill  loams  produced  1  ().">. 7 
per  cent  and  102.1  per  cent  of  the  cultivated,  while  the  day  loams 
and  clays  produced,  respectively,  !H..r>  per  cent  and  !>2.«!  per  cent 
as  much  as  the  cultivated.  \Yhcn  the  crop  becomes  large  enough  to 
partly  shade  the  soil,  and  the  roots  become  thoroughly  distributed 
through  the  soil,  there  is  very  little  necessity  for  cultivating  to 
conserve  moisture.  The  water  that  moves  upward  is  captured  by 
the  roots  before  it  reaches  the  surface  and  evaporates. 

Root  Injury. — Most  of  the  crops  grown  in  humid  regions  that 
require  cultivation  are  shallow  rooting.  A  large  supply  of  moisture 
and  plant  food  is  in  the  surface  soil.  The  roots  naturallv  develop 
23 


354 


SOIL  PHYSICS  AND  MANAGEMENT 


there  in  larger  numbers,  attracted  by  the  favorable  conditions  for 
obtaining  food  and  moisture.  An  examination  will  show  many  of 
the  roots  of  cultivated  plants  within  the  surface  three  inches  of 


Fio.   170. — Yields  of  corn  (field  weight)  with  different  methods  of  tillage.     (1911) 

soil  under  favorable  conditions  and  probably  three-fourths  of  the 
roots  of  the  plants  within  the  surface  or  plowed  soil. 


Fio.   171.— Yield  of  corn  (field  weight)  with  different  methods  of  tillage. 

To  preserve  these  roots  from  injury  very  shallow  cultivation 
must  be  practiced.  Roots  take  nourishment  from  the  soil  for  the 
plant  and  if  roots  are  cut  off  it  lessens  the  food  supply.  Not  only 
this,  but  it  takes  energy  from  the  plant  to  reproduce  the  roots  de- 


TILLAGE 


355 


stroyed.  Experiments  have  been  made  with  corn  to  show  the  effect 
of  cutting  the  roots  similar  to  what  is  done  in  cultivation  to  a 
depth  of  four  inches.  The  following  tahle  gives  the  results  obtained  : 

Results  of  Shallow  and  Deep  Cultivation  utui  Ituot  Pruning  of  Corn6    (Yields  in 
Buxhels  Per  Acre) 


Kind  of  cultivation 

1888 

1889 

1890 

1891 

1892 

1893 

1890 

Average 
for  years 
Riven 

1.  None  —  weeds  kept  down  by 
scraping  with  a  hoe  *  .... 
2.  Shallow—  4  or  5  times  ...... 
3.  Deep  —  4  or  5  times  

90.0 
93.8 
841 

77.1 

84.6 
74? 

69.1 
66.8 
608 

55.3 

58.4 
634 

76.8 
70.1 
80.1 

28.7 
36.3 
33.6 

87.0 
85.5 
83.4 

67.7 

70.8 
68.6 

4.  Shallow  —  roots  unpruned  .  .  . 
5.  Shallow  —  roots  pruned  t-  •  • 
6.  Scraped  with  how  *  

97.0 
91.0 
040 

90.9 

78.3 
85.8 

78.7 
55.0 
76.7 

70.0 

487 
66  3 

78.9 
70.7 

33.4 
26.2 

74.8 
61.6 
80.7 

7.  Scraped    with    hoe,*    roots 
pruned  t  

85.5 

68.4 

61.5 

39.7 

as.3 

*  No  mulch  produced. 

t  A  frame  one  foot  square  was  placed  over  tlie  hill  of  corn  and  a  knife  wa."  run  around 
the  outside  4  inches  deep. 

The  effect  of  cutting  the  corn  roots  is  shown  by  comparing  plots 
4  and  5,  where  a  difference  of  1;?.^  bushels  per  acre  is  shown  in 
favor  of  no  root  injury,  and  the  difference  is  about  the  same  when 
plots  fi  and  7  arc  compared. 

Level  Cultivation. — Under  practicallv  all  conditions  of  rainfall 
and  soils  almost  level  cultivation  is  most  desirable.  Kidired  cultiva- 


Fio.   172.— Lev. 


rultivation. 


356 


SOIL  PHYSICS  AND  MANAGEMENT 


tion  must  necessarily  be  deep,  and  is  always  accompanied  by  root 
injury.  In  some  alluvial  bottom  land  ridging  may  be  necessary. 
Where  the  annual  morning  glory  or  other  troublesome  weeds  are 
thick  deep  cultivation  may  be  advisable  to  cover  them,  especially 

r  - 


Fio.  173. — Ridged  cultivation  with  drilled  corn.     A  very  undesirable  method  with  nearly 

all  soils. 

if  the  corn  is  drilled  and  not  checked.  This  forms  a  very  strong 
objection  to  drilling  corn.  The  ridge  formed  is  sometimes  six  to 
eight  inches  high.  The  disk  cultivator  9r  the  little  diamond  plow 
are  both  used  for  ridging.  The  ideal  cultivation  is  not  absolutely 
level,  but  such  as  to  have  a  slope  of  one  to  two  inches  between  rows. 
Compare  figure  172  and  figure  173. 


QUESTIONS 

1.  What  was  Jethro  Tull's  theory  of  plant  nutrition? 

2.  Define  tillage. 

3.  Why  is  loosening  the  soil  necessary  ? 

4.  Give  results  obtained  for  plowing  and  not  plowing. 

5.  What  are  the  advantages  of  turning  under  vegetable  matter? 

6.  Give  advantages  of  killing  weeds. 

7.  Give  tillage  for  storing  and  conserving  moisture. 

8.  Why  is  compacting  necessary? 

9.  Give  action  of  mold-board  plow  in  turning  soil. 

10.  What  conditions  are  necessary  for  best  pulverization? 

11.  What  is  the  advantage  of  the  stubble  plow? 

12.  What  is  the  objection  to  using  it  in  plowing  sod? 

13.  Describe  the  general  purpose  plow. 

14.  Describe  the  sod  plow  and  its  work. 


TILLAGE  357 

15.  What  is  the  hillside  plow? 

10.  What  are  the  ad  vantages  of  the  disk  plowT 

17.  What  is  the  use  of  the  lister? 

18.  Describe  the  subsoil  plow  and  give  its  use. 

19.  (Jive  points  of  difference  in  the  kinds  of  harrows. 

20.  What  are   the  advantages   of   the  disk    harrow    that   make   it   so   uni- 

versally used  ? 

21.  Why  is  it  necessary  to  use  coin  patters? 

22.  What  are  the  objections  to  the  drum  roller? 

23.  (Jive  advantages  of  other  forms  of  roller. 

24.  What  is  a  planker  and  for  what  used  ? 

25.  Describe  the  Campbell  subsurface  packer. 
20.  What  are  its  advantages? 

27.  (Jive  three  classes  of  cultivators. 

28.  (Jive  advantages  and  disadvantages  of  each. 

29.  Which  is  best  adapted  to  shallow  cultivation? 

30.  (Jive   value  of  different  seeders  as  tillage   implements. 

31.  (Jive  four  points  in  good  plowing. 

32.  What  determines   the   time   of   plowing? 
.33.  What  can  you  say  about  fall  plowing? 

34.  May  the  soil  become  too  dry  to  plow  in  the  full? 

35.  (Jive  advantages  of  fall  plowing. 

30.  What  soils  are  most  benefited  by  fall  plowing? 

37.  What  are  some  advantages  of  spring  plowing? 

38.  What  preparation   should  be  made  for  spring  plowing? 
30.  How  deep  should   plowing  be  done? 

40.  What  can  be  said  of  extremely  deep  plowing  in  humid  regions? 

41.  Tell  about  the  results  from  subsoil  ing. 

42.  What  may  be  said  in  favor  of  dynamiting? 

43.  What  is  the  effect  of  deep  rooting  crops? 

44.  What  are  the  advantages  of  a  good  seed  bed? 

45.  What  are  the  objections  to  clods? 

40.  (Jive  the  facts  in  regard  (o  a  good  se<-d  bed  for  wheat. 

47.  What  are  the  conclusions  from  the  table  page  347? 

48.  How  should  the  need  bed  be  prepared  for  corn  from  fall-plowed  land  .' 
4!).  fJive  method  of  preparing  seed  from  spring-plowed  land. 

50.  Tell  about  seed  bed  for  oats. 

51.  What  are  the  objects  to  be  attained  in  the  cultivation  of  a  crop? 

52.  Give  results  of  weeds  on  yield  of  corn  at  the  Illinois  Station. 

53.  What   is   the  value  of  the   mulch    in   growing  corn    as   shown   by    crop 

yields? 

54.  fJive  results  of  the  Department  <>f  Agriculture  on  cultivation   of  corn. 

55.  What  effect  does   root  injury  by  cultivators   have  on  yield   of  corn? 

REFERENCES 
1  Mosier.  J.   G.,  and   Gustafson.   A.    K..   Bulletin    181.    Illinois   Station.   Soil 

Moisture  and  Tillage  for  Corn.  1!H">.  p.  585. 
'Call.    L.    K.,    Bulletin    18."),    Kansas    Station,    Preparing   Land    for    Wheat. 

1913,   p.   0. 

'Illinois  Bulletin  181  (as  above),  p.  r>70. 
4  Illinois  Bulletin  181  (as  alnive).  p.  "»8-J. 
3Cates,  J.  S.,  and  Cox,  11.  K,  Bulletin  2.'»7.  Bureau  of  Plant  Industry. 

1T.  S.  D.  A.,  The  Weed  Factor  in  the  Cultivation  of  Corn.  1!»!2. 
•Morrow,  (J.  W.,  Results  given  in  Illinois  Bulletin  181    (as  above)   p.  "i(!S. 


CHAPTER    XXVII 

SOIL  EROSION 

EROSION  is  the  removal  of  soil  material  by  air  or  water  in 
motion.  The  work  of  water  alone  will  be  considered  in  this  chapter. 
The  National  Conservation  Commission  1  states  that  "  on  the  basis 
of  estimates  received  from  30,000  farmers,  representing  every 
county  in  the  United  States,  10,622,000  acres  of  farm  land  have 
been  abandoned,  and  that  3,888,000  acres,  or  0.2  per  cent,  have  been 
devastated  by  soil  erosion."  Large  areas  in  the  states  from  Penn- 
sylvania to  Georgia  and  westward,  including  Kentucky,  Tennessee, 
Alabama,  Missouri,  Arkansas,  Louisiana,  and  Mississippi,  are  sub- 
ject to  serious  damage  by  erosion.  Even  such  prairie  states  as  Illi- 
nois and  Iowa  suffer  loss  in  this  way.  As  an  average  of  the  sixty- 
one  -counties  of  Illinois,  of  which  a  detailed  soil  survey  has  been 
made,  it  has  been  found  by  actual  measurement  of  the  soil  areas 
that  about  17  per  cent  is  hilly  and  subject  to  serious  erosion. 

Cause  of  Erosion. — Erosion  occurs  whenever  rain  falls  on  un- 
protected- sloping  land  so  rapidly  or  in  such  quantities  that  the  soil 
cannot  absorb  the  water  as  fast  as  it  falls.  The  same  is  true  of  the 
melting  snow.  Only  that  water  lost  from  the  surface — the  run-off— 
causes  erosion.  The  run-off  depends  on  (1)  the  slope  or  topography 
of  the  land,  (2)  the  texture  and  structure  of  the  soil,  (3)  the  vege- 
tative covering,  and  (4)  the  character  of  the  precipitation. 

1.  Effect   of  Topography. — The  run-off  from   mountain   to- 
pography is  from  one-third  to  three-fourths  of  the  total  annual 
rainfall  when  it  varies  from  15  to  40  inches.    Newell  estimates  the 
run-off  from  the  basin  of  the  Savannah  river  to  be  48.9  per  cent 
(eight-year  average)  of  the  annual  rainfall;  56.5  per  cent  from  the 
Connecticut  valley   (13-year  average),  and  53  per  cent   (six-year 
average)  from  the  Potomac  basin.     Greenleaf  places  the  loss  from 
the  broad  level  to  undulating  basin  of  the  Illinois  river  at  24  per 
cent,  and  Leverett  2  gives  21  per  cent  as  the  amount  of  run-off  from 
Illinois  as  a  whole.    The  run-off  of  the  United  States  as  a  whole  is 
estimated  at  one-third  of  the  annual  rainfall. 

2.  Texture  and  Structure  of  the  Soil. — Coarse  soils  absorb 
a  much  larger  proportion  of  the  rainfall  than  do  the  fine-grained 
ones.    The  rate  of  absorption  depends  on  the  size  of  pores,  not  on 

358 


SOIL  EROSION 


359 


the  total  pore  space  in  the  soil.  This  fact  explains  the  rapid  ab- 
sorption by  the  coarse-grained  soils  and  the  slow  action  of  the  line- 
grained  ones.  However,  if  the  latter  are  loose  and  open  from 
recent  tillage  their  absorption  compares  favorably  with  that  of 
coarser  soils.  Unless  the  finest-grained  soils  (clay  loams  and  clays) 
are  exceptionally  well  supplied  with  organic  matter  and  limestone 
the  beating  of  raindrops  breaks  down  the  granules,  diminishing  the 
size  of  the  pores,  thus  rendering  the  soil  less  absorbent.  As  a  result 
a  large  amount  of  water  is  lost  from  even  moderate  slopes. 

3.  Vegetative  Covering. — The  surface  soil  of  a  natural  forest 
is  usually  covered    with  leaves  and   twigs,  which  protect  it  from 


Fio.   174. — Two  hundred  s<|u:ire  miles  <>l  mi-i-  forested  mountains  in  China,  which  a  cen- 
tury ago  paid  rich  revenue  mi  ihcir  lumber  product,    (Bailey  Willis.) 

erosion.  It  suffers  little  so  long  as  this  natural  protection  remains 
undisturbed  (Fig.  171).  Natural  prairies  are  usually  protected  in 
this  way  by  a  good  sod  of  native  grass.  The  rain  drops  do  not 
usually  strike  the  soil  direct  and  thus  destroy  the  granules,  as  they 
tend  to  do  in  cultivated  fields.  When  this  covering  which  nature 
provided  is  removed  or  destroyed  erosion  takes  place. 

4.  Character  of  the  Rainfall. — A  gentle  rain  will  be  absorbed 
entirely  by  almost  all  soils,  since  it  does  not  come  more  rapidly  than 
the  water  can  percolate  through  the  soil,  thus  preventing  complete 
saturation  of  the  surface.  A  heavy  rain  falling  on  medium-  or  fine- 
grained soils  soon  saturates  the  surface  and  then  absorption  bv  the 
soil  cannot  take  place  anv  faster  than  percolation  from  the  surface 

I  •  I 

into  the  lower  strata. 

Results  of  Erosion. —  It  is  quite  impossible  to  determine  with 


360  SOIL  PHYSICS  AND  MANAGEMENT 

any  degree  of  accuracy  the  total  quantity  of  material  moved  by 
water,  but  it  must  be  many  times  as  much  as  is  deposited  from  sus- 
pension in  lakes  and  the  seas. 

Some  geologists  hold  that  the  land  surface  of  the  earth  as  a 
whole  is  being  lowered  by  erosion  one  foot  in  six  thousand  years. 
The  combined  loss  from  surface  erosion  and  from  solution  by 
ground  waters  amounts  to  one  foot  in  about  4100  years. 

When  a  stream  emerging  from  a  narrow  valley  spreads  out  over 
the  bottom  land,  the  velocity  of  the  water  is  checked  and  its  load 
of  stones,  gravel  and  sand  is  deposited  on  the  rich  alluvial  land.  In 
this  way  much  valuable  soil  is  buried  completely  by  material  of  little 
immediate  use  to  plants.  The  finer  material,  if  unweathered  and 
deficient  in  organic  matter,  may  be  almost  equally  worthless  until 
acted  upon  by  the  regular  soil-forming  agencies.  If  the  deposition 
is  rapid  there  is  little  chance  for  soil  to  form,  but  if  deposition  is 
prevented  for  a  time  this  almost  worthless  material  becomes  a  valu- 
able soil. 

1.  Removal  of  Organic  Matter  and  Nitrogen. — The  surface 
soil  contains  the  greater  part  of  the  organic  matter,  and  so  is  the 
richest,  most  productive  part  of  the  soil.  The  removal  of  any  ap- 
preciable amount  of  this  stratum  reduces  the  amount  of  plant  food, 
especially  the  nitrogen,  rendering  the  soil  less  productive  than 
formerly.  The  following  results  from  pot  culture  tests  in  the  green- 
house show  their  great  need  of  nitrogen : 

Yields  from  Eroded  Hill  Lands3  (Bushels  per  Acie) 


Treatment 

Pulaski 
county 
wheat 

Henry  county 
oats 

None  

8 

21 

Potassium  

9 

23 

Phosphorus  

9 

31 

Nitroeen  .  . 

69 

225 

2.  Changes  Physical  Character  of  Soil. — The  removal  of  the 
surface  soil  exposes  the  yellowish  or  reddish  subsoil,  which  is  heavier 
and  more  difficult  to  work  than  the  original  surface  soil.  These 
exposures  of  subsoil  are  locally  known  as  "  clay  points."  They  are 
less  productive  than  the  original  land.  In  some  residual  and  glacial 
soils  with  a  wide  range  in  size  of  particles  the  texture  of  the  sur- 
face may  be  changed  from  a  fairly  heavy  to  a  sandy  or  gravelly 
soil  by  the  removal  of  the  silt  and  clay,  leaving  only  the  coarse  mate- 
rial which  was  too  large  to  be  carried  away  by  the  water. 


SOIL  EROSION 


361 


3.  Changes  of  Color. — Erosion  almost  invariably  results  in  a 
change  of  color  of  the  soil.  If  the  soil  is  brown,  yellow  or  grayish 
yellow,  erosion  produces  a  yellow  or  reddish  color,  depending  wholly 
on  the  color  of  the  subsoil.  On  the  Piedmont  Plateau  and  some 
other  residual  soil  areas  the  color  becomes  very  red,  due  to  exposure 
of  the  subsoil. 

KINDS   OF   KROSIOX 

Two  somewhat  distinct  types  of  erosion  are  recognized,  sheet 
erosion  and  gullying. 

I.  Sheet  Erosion 

Water  flowing  over  a  uniform  slope  removes  approximately  the 
same  amount  of  soil  material  from  all  parts.  Sheet  erosion  is  the 
source  of  far  greater  loss  than  gullying.  The  latter  quickly  and 
completely  ruins  small  areas,  but  the  former  reduces  the  produc- 
tiveness over  large  areas  to  the  point  of  unprofitable  returns. 

Methods  of  Prevention  and  Reclamation. —  1.  Application 
cf  Limestone. — Limestone  in  time  renders  the  soil  more  porous 


1  in  Marrli,  photngrnphml  in 


bv   producing  granules.     This  lessens  erosion,  because   the  soil    i- 
more  absorbent  and  the  heavier  compound  granules  ;ire  more  difti- 


362  SOIL  PHYSICS  AND  MANAGEMENT 

cult  to  move  than  the  individual  particles.  The  more  important 
effect  of  limestone,  however,  lies  in  its  power  of  correcting  acidity, 
rendering  the  soil  more  favorable  for  the  growth  of  legumes  which 
furnish  organic  matter  and  nitrogen  (Fig.  175),  also  for  soil-bind- 
ing crops,  such  as  timothy  and  bluegrass. 

2.  Protection  by  Crops. — The  surface  of  rolling  land  should 
be  kept  covered  with  soil-binding  crops  as  much  of  the  time  as 
possible.  For  this  purpose  meadows,  pastures  and  catch  and  cover 
crops  are  indispensable  in  the  farming  of  rolling  lands. 

(a)  Meadows  and  Pastures. — The  perennial  grasses,  timothy  in 
the  northern  states  and  red  top  and  Bermuda  grass  further  south j  on 
acid  soils  are  good  meadow  grasses.     Bermuda  grass  makes  good 
pasture  and,  if  cut  early  enough,  fairly  good  hay.     Its  growth  is 
such  as  to  stop  washing  very  well.    It  is  more  profitable  to  grow  one 
or  more  legumes  with  the  grasses,  as  the  latter  use  nitrogen  fixed 
by  the  legume.    This  is  particularly  desirable  on  those  soils  deficient 
in  nitrogen.    Together  these  plants  form  a  good  sod,  which  protects 
the  surface  and  holds  the  soil  together. 

Much  of  these  hilly  lands  should  never  be  plowed,  but  kept  in 
pasture.  Blue  grass,  timothy,  red  top  and  other  grasses,  together 
with  red,  alsike  and  white  clover,  sweet  clover  (Melilotus  alba),  and 
Japan  clover  (Lespedeza  striata),  may  be  seeded  in  addition  to 
native  grasses  that  follow  upon  the  removal  of  the  forest.  One  or 
more  of  these  should  be  able  to  get  a  good  foothold  regardless  of 
whether  the  soil  is  acid  or  contains  Jimestone.  These  legumes 
enable  the  grasses  to  make  a  much  better  sod.  As  already  pointed 
out,  legumes  in  general  require  a  soil  containing  limestone  for  good 
growth.  Japan  clover,  however,  seems  to  be  indifferent.  Sweet 
clover  is  more  successful  than  any  of  the  other  clovers  under  very 
unfavorable  conditions  if  its  two  requirements — rthorough  inocula- 
tion and  abundance  of  limestone — are  satisfied.  It  makes  a  strong 
growth  and  may  be  pastured  or  grown  for  hay  and  seed.  Blue  grass 
soon  starts  in  it,  living  in  part  on  nitrogen  fixed  by  the  legumes. 
This  increases  the  amount  of  pasture  afforded  and  forms  a  better 
protection  for  the  soil. 

(b)  Catch  and  Cover  Crops. — Cultivated  land  should  not  be 
left  unprotected  throughout  the  winter  and  spring  months,  especially 
in  those  sections  where  the  soil  is  not  frozen  during  any  consider- 
able part  of  the  winter.     Cowpeas  or  soybeans  may  be  seeded  be- 
tween the  rows  of  corn  at  the  last  cultivation  or  between  the  trees 
in  orchards.     Hairy  or  winter  vetch  and  Japan  clover  are  more 


SOIL  EROSION  363 

desirable  in  some  places,  especially  the  vetch,  as  it  lives  through 
the  winter  and  begins  growth  early  in  the  spring.  With  fall  sown 
cereals  sweet  clover  may  be  used  to  good  advantage  when  the  soil 
is  well  supplied  with  plant  food.  Wheat,  rye  and  winter  oats  cover 
the  ground  well  and  the  roots  are  a  very  effective  soil  binder.  Vetch 
and  Japan  clover  are  probably  most  desirable  when  sufficient  growth 
is  made,  because  of  their  ability  to  gather  nitrogen,  the  increase  of 
which  is  most  essential  in  the  improvement  of  these  soils.  Crab 
grass  is  a  natural  cover  in  seasons  of  normal  rainfall,  as  it  makes 
sufficient  growth  to  serve  well  as  a  surface  protection,  especially  in 
corn  and  old  wheat  fields.  • 

3.  Residues. — Stalks  of  corn   or  cotton  may  be  harrowed  or 
rolled  down  after  the  crop  is  harvested.     Tn  this  way  they  help  to 
protect  the  soil  from  the  beating  of  rain  drops  and  reduce  some- 
what the  amount  of  thawing  in  winter  and  early  spring.    When  the 
surface  soil  is  thawed  for  an  inch  or  two,  it  is  easily  eroded. 

It  is  desirable,  also,  to  cover  badly  eroded  areas,  or  areas  where 
erosion  is  especially  rapid,  with  straw  of  grain  or  clover,  manure, 
or  other  coarse  material.  These  areas  are  unusually  low  in  organic 
matter,  as  more  or  less  of  the  surface  soil  has  been  removed.  The 
coarse  organic  matter  will  not  only  hold  the  soil  in  place,  but  supply 
plant  food  to  succeeding  crops. 

4.  Increasing  the   Organic   Matter. — Most   lands   subject   to 
serious  erosion  have  been  timbered  and  are  naturally  low  in  organic 
matter  and  nitrogen.    .The  hilly  timber  lands  of  Illinois  contain 
an  average  of  1.5  pop  cent  or  15  tons  of  organic  matter  in  the  sur- 
face soil  (two  million  pounds  per  acre).   The  yellow  silt  loam — hilly 
timber   land — of    llardin    County,4    Illinois,    which    represents   the 
unglaciafed  loess-covered  section  of  the  states  adjoining  the  lower 
Ohio  and  the  middle  section  of  the  Mississippi  river,  contains  as  an 
average  of  15  analyses  1.1  per  cent  or  1  1  tons  of  organic  matter  in 
the  surface  soil.     The  hill  soils  of  the   Piedmont    Plateau.  Appa- 
lachian   Mountain    Plateau,   and    Limestone    Vallevs   and    Upland 
Provinces  contain  from  one-half  to  two  and  one-half  per  cent  of 
organic  matter/'     The  average  organic-matter  content   is  about   1.1 
per  cent/'      Profitable  crops   cannot    be   produced    without    adding 
considerable  organic  matter  or  nitrogen. 

Besides  furnishing  nitrogen,  organic  inafter  aids  granulation 
and  cements  the  finer  particles  together  into  compound  granules, 
as  discussed  under  organic  matter.  These  soils  need  the  addition  of 
large  quantities  of  organic  matter  to  enable  the  surface  to  absorb 


364 


SOIL  PHYSICS  AND  MANAGEMENT 


and  retain  more  of  the  rainfall.  Owing  to  its  granulating  effect 
organic  matter  reduces  the  tendency  to  run  together  and  keeps  the 
soil  open,  so  there  is  less  run-off  and  less  erosion. 

Legumes  must  have  a  large  place  in  the  agriculture  of  these 
lands.  It  is  advisable  to  feed  most  crops  to  stock  on  the  farm.  All 
the  manure  produced  should  be  carefully  preserved  and  returned  to 
the  soil.  All  stalks,  straw,  stubble  or  other  residues  not  fed  should 
be  plowed  under.  Plow.ing  under  the  entire  crop  of  cowpeas,  or  at 
least  the  straw,  is  a  practice  to  be  recommended. 

5.  Deep  Contour  Plowing. — A  loose  soil  has  more  pore  space 
than  a  compact  one,  consequently  it  will  absorb  more  water.  A 

' 


Fia.  176. — Cultivated  terraces  in  China.     (Bailey  Willis.) 

silt  loam  in  loose  open  condition  will  absorb  10  to  15  per  cent  more 
water  than  when  compact.  The  pores  in  a  compact  soil  are  so  small 
that  it  absorbs  rain  very  slowly  and  much  of  the  water  is  lost  as 
run-off.  The  surface  soil  may  be  kept  loose  by  plowing  to  a  depth 
of  eight  to  ten  inches.  Eight  inches  of  loose  silt  loam  fairly  well 
supplied  with  organic  matter  is  capable  of  absorbing  two  inches  of 
water.  While  a  greater  depth  of  plowing  would  increase  the  storage 
capacity,  experiments  show  such  to  be  unprofitable.  The  Georgia 
Station  6  reports  results  which  indicate  that  plowing  more  than 
eight  inches  deep  lessens  the  yield  of  cotton.  It  is  believed,  how- 
ever, that  loessial  soils  may  be  plowed  to  a  greater  depth  with  profit. 
Plowing  on  sloping  land  is  best  done  across  the  slope  with  a 


SOIL  EROSION 


365 


reversible  or  hillside  plow,  by  which  all  of  the  soil  may  be  turned 
in  the  same  direction.  In  ordinary  plowing  up  and  down  the  hill 
the  small  depressions,  nearly  always  found  between  furrows,  and 
especially  the  dead  furrows,  serve  as  places  whore  the  water  col- 
lects and  erosion  begins.  In  contour  plowing  these  ordinary  de- 
pressions are  at  right  angles  to  the  slope  and  retard  rather  than 
encourage  erosion.  When  the  reversible  plow  is  used  there  are  no 
dead  furrows  except  on  the  crest  of  ridges  where  there  is  but  little 
danger  of  erosion. 

(5.  Contour  Seeding. — Corn  and  cotton  should  be  planted  on 
contour  lines  or  nearly  so.  This  reduces  the  danger  of  erosion  in 
planter  tracks,  and  the  cultivation  will  be  across  the  slope,  which 
will  avoid  the  formation  of  small  gullies  between  the  rows.  For 
this  reason  the  seeding  of  oats,  wheat  and  cowpeas  should  be  across 
the  slope,  particularly  when  the  drill  is  used. 

7.  Terraces. —  In  those  sections  where  intensive  farming  is  prac- 
ticed and  in  fruit  districts  where  the  rain  falls  in  heavy  showers  and 
the  soil  does  not  absorb  water  readily,  terracing  is  practiced  to  good 
advantage  (Fig.  17(>).  Three  types  of  terraces  are  in  common  use — 
the  guide  row,  the  level  bench  and  the  Mangum. 

(a)  The  Guide  Ron)  (Fig.  177)  is  made  by  throwing  four  fur- 
rows together  on  contour  lines,  with  an  interval  of  approximately 


Flo.    177. — Guide-row  terraces.     There  is  no  slope  from  one  end   of  a  terrnre   to   the  other, 
but  there  is  a  slight  slope  from  the  back  of  a  terrace  to  the  front.     (IVarce,  R.  R.) 

three  feet  in  altitude  between  the  rows.  This  makes  a  low  Hat  ridge, 
and  in  order  to  avoid  any  waste  of  land  a  row  of  the  crop  niav  be 
planted  on  it.  This  method  of  terracing  is  employed  on  slopes  thai 
do  not  exceed  1<>  per  cent,  or  one  foot  in  ten.  and  where  the  soil 
is  open,  absorbing  the  rainfall  readily. 


366 


SOIL  PHYSICS  AND  MANAGEMENT 


(b)  The  Level  Bench  (Fig.  178)  is  employed  on  steeper  slopes. 
These  may  be  developed  from  the  guide-row  or  laid  out  on  contours 
by  using  a  reversible  plow.  By  plowing  down  hill  a  level  bench  is 
developed  in  a  few  ye#rs.  When  the  desired  form  of  the  terrace 
has  been  produced  it  is  well  to  throw  the  soil  up  the  slope  as  often  as 
down  in  order  to  avoid  exposing  too  much  unproductive  subsoil  at 
the  upper  side  of  the  terrace.  Each  bench  must  be  cultivated  as  a 
separate  unit,  and  driving  over  the  bank  or  outer  edge  must  be 
avoided  lest  depressions  be  made  which  result  in  gullies.  The 
growth  of  weeds  on  the  edge  of  the  bench  should  be  prevented  and 


Fia.  178. — Level-bench  terrace.     (Bui.  236,  North  Carolina  Station.)      (F.  R.  Baker.) 

a  good  grass  covering  encouraged  to  prevent  erosion.  Crops  may  be 
grown  in  straight  TOWS  or  on  contours  following  the  terrace  lines. 
Most  farmers  object  to  the  short  rows,  which  are  necessary  if  the 
rows  are  to  be  kept  straight,  because  of  the  loss  of  time  and  the 
tramping  out  of  part  of  the  crop  in  turning  during  cultivation. 
Undoubtedly  the  best  way  to  prevent  erosion  while  farming  these 
lands  is  to  plant  and  cultivate  across  the  slope  or  parallel  to  the 
terrace.  The  uncultivated  bank  growing  weeds  or  grass  is  a  serious 
objection  to  this  form,  as  it  is  a  breeding  place  for  injurious  insects 
and  a  home  for  moles,  mice  and  other  animals.  Very  often  tl  o 
water  from  the  slope  above  finds  its  way  into  one  of  their  burrows 
and  a  considerable  gully  forms  in  a  short  time.  A  terraced  park 
is  shown  in  figure-179. 

(c)   The  Mangum  Terrace  (Fig.  180)  is  a  very  desirable  form, 
because  it  eliminates  the  uncultivated  spaces  of  the  level  bench.       It 


SOIL  EROSION 


367 


I 


Fio.  179. — A  torraccd  park  in  Mississippi.  While  the  natural  slope  wns stable  under  the 
protection  of  the  virgin  forest,  it  was  necessary  to  terrace  to  prevent  devastating  erosion 
when  the  land  was  cleared.  (Bureau  of  Soils,  I".  S.  D.  A.,  Hul.  71.) 


FIG.  ISO. --The  ManRum  terrace.    With  this  form  there  is  no  wasteland.    (I'.S.  Dopt.  of  Agr.) 


368 


SOIL  PHYSICS  AND  MANAGEMENT 


differs  from  the  guide  row  and  level  bench  in  that  the  lines  are  not 
level,  but  are  run  across  the  slope  with  a  grade  of  six  to  ten  inches 
in  100  feet  towards  some  natural  outlet  into  which  the  water  may 
drain.  The  terrace  is  made  by  plowing  several  furrows  along  the 


Fio.   181. — Locusts  growing  on   eiillied   land.      The   gullies  have  been   almost  completely 

filled.     (Heaton.) 

surveyed  line  and  pulling  the  soil  to  the  lower  side  so  as  to  form 
a  low  dyke  or  ridge  with  a  shallow  depression  just  above  it.  The 
crop  is  planted  obliquely  over  the  dyke  and  terrace,  so  that  water 
may  collect  along  the  rows  and  be  conducted  into  this  depression, 


SOIL  EROSION  369 

or  wide  bottomed  ditch,  which  has  but  slight  fall,  so  there  will  be 
little  or  no  erosion.  The  Mangum  terrace  can  be  used  to  good  ad- 
vantage on  heavy  soils  which  absorb  water  very  slowly.  This  form 
provides  very  effective  protection  against  erosion  and  eliminates 
waste  land. 

8.  Reforesting. — As  already  pointed  out,  the  soil  of  virgin  for- 
ests is  protected  by  leaves  and  twigs.  On  cleared  areas  where  the 
surface  soil  has  been  removed  to  such  an  extent  that  it  does  not 
produce  profitable  crops  and  especially  where  gullied  it  may  be 
advisable  to  imitate  nature  by  planting  trees.  The  black  locust  is 
excellent  for  this  purpose.  Being  a  legume  it  is  capable  of  good 
growth  on  soils  very  low  in  organic  matter.  The  leaves  and  twigs 
protect  the  soil  and,  through  the  aid  of  nitrogen  fixed  by  the  legume, 
grasses  soon  start  among  the  trees  (Fig.  181 ).  By  this  time  there  is 
little  movement  of  soil  material.  When  abandoned,  such  areas  are 
reforested  naturally,  but  the  process  is  very  slow  and  much  ad- 
ditional erosion  may  take  place  before  there  has  been  sufficient 
growth  to  hold  the  soil.  The  natural  growth  in  most  caws  will  be 
of  far  less  value  than  the  black  locust  or  other  trees  which  might  be 
selected  for  this  purpose. 

J).  Tiling. — In  rolling  sections,  "  seepy  "  or  "springy"  spots 
are  common.  On  these,  crops  do  poorly,  wheat  often  "  heaves  "  and 
may  be  killed  completely.  In  wet  seasons  these  spots  are  much 
larger  than  normal,  so  the  damage  is  much  greater.  In  many  of 
these  places  and  on  much  rolling  land  which  does  not  have  an 
especially  pervious  subsoil,  tile  will  produce  all  its  ordinary  bene- 
fits, including  warmer,  drier  surface  soil  in  (he  spring  when  early 
tillage  and  planting  are  desirable.  The  most  beneficial  effect  of 
tiling  is  the  increase  in  perviousness  of  the  soil,  so  that  the  rains 
are  absorbed  more  readily,  thus  decreasing  the  run-off.  This  is  a 
very  effective  method  of  preventing  erosion,  but  the  expense  is  al- 
most prohibitive  when  that  is  the  only  purpose  to  be  accomplished. 

II.  Gullying 

In  any  depression  extending  up  and  down  a  slope  water  col- 
lects. Its  velocity  is  increased  with  its  volume,  as  is  also  it<  trans- 
porting and  eroding  power.  For  this  reason  depressions  extend- 
ing down  the  slope,  such  as  a  furrow,  wagon  or  planter  track,  a 
sheep  or  cow  path,  or  even  a  mole  tunnel,  may  soon  result  in  a  small 
gully.  These  should  be  filled  with  some  coarse  organic  matter  or 
24 


370 


SOIL  PHYSICS  AND  MANAGEMENT 


obliterated  in  other  ways.  Otherwise,  each  rain  will  increase  their 
size  and  they  will  become  a  permanent  source  of  trouble.  In  a 
few  years  considerable  areas  will  be  ruined.  Gullying  in  different 
degrees  is  seen  in  figures  182,  183,  and  184. 

Methods    of    Prevention    and    Filling.— 1.  Straw-brush.— 


Fia.  182. 


Fio.  183. 

Fia.   182. — Erosion  in  pasture  near  crest  of  slope. 
Fio.   183. — Old  field  erosion  in  Mississippi. 

Gullies  should  be  filled  with  a  durable  material  sufficiently  open 
to  allow  the  water  to  pass  through  it  and  yet  reduce  the  velocity  of 
the  current  so  as  to  cause  deposition.  The  material  best  suited 
depends  on  conditions.  If  the  slope  ^is  gentle  and  the  quantity  of 
water  small,  straw,  weeds,  or  anything  of  that  nature  holds  the  soil, 
that  would  otherwise  be  lost,  partially  filling  the  gully.  Where  the 
t 


SOIL  EROSION 


371 


slope  is  steeper  or  the  amount  of  water  greater,  steps  must  be  taken 
to  [>  re  vent  the  rapidly  flowing  water  from  washing  away  the  mate- 
rial used.  For  this  purpose  stakes  slanting  up  hill,  driven  through 
the  straw  are  used  successfully.  Hedge  or  other  brush  (Fig.  185) 
placed  on  the  straw  help  to  hold  it.  Stones  may  well  be  used  for 
this  purpose,  especially  if  they  occur  on  adjoining  slopes. 

Stock  frequently  make  paths  up  and  down  steep  slopes  to  such 
an  extent  that  the  grass  is  killed  and  a  slight  depression  produced. 
Water  collects  in  this  during  rains  and  a  gully  is  started. 

In  pasture  lauds,  waterfalls  sometimes  occur  that  move  up  the 


slope  by  means  of  headwater  erosion  (Fig.  1S(5).  As  water  goes 
over  the  fall  it  undermines  the  sod  surface,  which  then  caves  in. 
making  a  gully  which  is  especially  dillicult  to  fill.  In  such  places 
it  is  necessary  to  protect  the  face  of  the  bank  from  the  undermining 
action  of  the  water.  This  may  be  done  by  tilling  the  gully  at  the 
fall  with  brush  or  straw  or  both,  which  must  be  held  in  place  by 
stakes  or  heavy  material,  such  as  stones.  Since  the  water  from 
•pasture  land  contains  but  little  sediment,  filling  of  gullies  under 
these  conditions  is  a  verv  slow  process.  For  completely  filling  the 
gullv,  dams  of  sonic  kind  must  be  used  below  the  fall. 

2.   Dams. —  In    cultivated    fields    earth   and    concrete   dams   are 
used  for  filling  large  irullies.    The  curlli  <!<ini  is  built  over  a  la  rue  tile 


372 


SOIL  PHYSICS  AND  MANAGEMENT 

Fia.  185. 


Fia.  186. 

FIG.  185. — Brush  checking  erosion. 
Fia.   186. — Headwater  erosion. 


Fio.  187. — Earth  dam  for  checking  erosion. 


SOIL  EROSION 


373 


laid  in  the  gully  to  be  filled.  A  vertical  tile  connects  with  the 
horizontal  one  a  few  feet  above  the  dam.  This  form  of  dam  is 
adapted  to  comparatively  small  gullies  of  slight  fall  which  do  not 
carry  large  amounts  of  water. 

The  dam  holds  the  soil  material  carried  down  by  the  stream 
and  the  water  which  would  otherwise  overflow  the  dam  and  ruin  it 
passes  down  through  the  vertical  tile  and  out  through  the  horizontal 
one.  The  arrangement  of  the  tile  is  shown  in  figure  1H7. 

Concrete  dams  are  better  adapted  to  large  gullies  carrying  a 


Fio.   IRS.— Filling  n  cully  1>\ 


if  a  cnncrcto  d:\ni. 


large  volume  of  water.  They  should  he  placed  well  into  the  bed 
of  the  gully  and  extended  into  the  Imnk  well  hack  from  the  gully 
{Fig.  IKS).  The  concrete  should  be  thoroughly  reinforced.  A  spill- 
way with  an  ample  concrete  floor  below  the  dam  is  absolutely  nec- 
essary to  prevent,  the  water  which  passes  over  from  undermining 
it.  The  vertical  tile  is  sometimes  used  as  with  the  earth  dam.  hut 
it  is  not  so  essential,  hut  the  horizontal  tile  should  he  used  for 
draining  the  temporary  pond  above  the  dam. 


374  SOIL  PHYSICS  AND  MANAGEMENT 

3.  Vegetation. — Among  the  many  plants  that  may  be  used  to 
excellent  advantage  in  checking  the  deepening  and  widening  of 
gullies,  the  black  locust  is  probably  the  most  valuable  tree.    Gullied 
soils  are  always  low  in  nitrogen,  yet  the  locust  thrives  in  spite  of 
this  fact.    The  roots  help  to  hold  the  soil  and  the  leaves  and  twigs 
also  offer  some  protection.     The  locust  adds  some  nitrogen,  to  the 
soil  and  grasses  soon  get  a  footing,  which  then  catches  the  finer 
material.     The  gully  may  be  almost  entirely  filled  in  this  way. 
Locust  trees  are  valuable  for  posts  if  not  attacked  by  borers.    Wil- 
lows and  cottonwoods  and  a  few  other  trees  may  be  used  in  the 
same  way,  but  their  wood  is  of  less  value  and  few,  if  any,  of  them 
possess  the  advantages  of  the  locust.      (See  Fig.  181,  page  368.) 

Timothy,  blue-grass,  redtop,  sweet  clover,  Japan  and  other 
clovers  are  very  useful  in  all  gullies,  but  more  especially  in  wide, 
flat-bottomed  ones  where  erosion  is  not  so  severe  as  to  prevent 
them  from  getting  a  good  start. 

In  many  localities  the  sod  of  blue-grass  or  tim&thy  in  draws  is  not 
disturbed  when  the  field  is  plowed  for  corn.  Where  limestone  is 
applied  or  where  its  roots  can  reach  carbonates  in  the  subsoil  sweet 
clover  is  exceptionally  valuable  because  of  its  strong,  rapid  growth. 
On  the  steep  limestone  slopes  of  Kentucky  sweet  clover  has  reclaimed 
large  areas  of  abandoned  land  which  now  produce  excellent  pasture 
and  large  crops  of  seed. 

4.  Filling  with   Soil. — On  more  gently   sloping  land  gullies 
may  be  filled  with  soil  by  means  of  plows  and  scrapers.     This 
method  can  'be  employed  with  profit  only  on   those  areas  where 
more  or  less  intensive  agriculture  is  to  be  practiced  or  where  filling 
a  few  small  gullies  in  this  way  will  reclaim  considerable  areas. 
Much  subsoil  will  be  on  the  surface  which  will  be  very  unproductive. 
Legumes  must  be  grown  for  supplying  organic  matter  and  nitrogen, 
thus  restoring  fertility.    If  the  soil  is  acid  cowpeas  is  the  best  crop 
to  grow.     If  the  soil  contains  limestone. or  if  limestone  is  applied 
sweet  clover  is  one  of  the  best  legumes  for  the  soil,  as  it  grows  under 
very  adverse  conditions.     Whichever  crop  is  grown  should  be  re- 
turned to  the  soil.    Figure  175,  page  362,  shows  sweet  clover  grown 
under  the  above  conditions. 

QUESTIONS 

1.  How  much  land  has  been  abandoned  in  the  United  States  T 

2.  What  percentage  in   Illinois   is   hilly? 

3.  How  do  other  states  compare  with  Illinois  in  this  respect? 

4.  Upon  what  does  run-off  depend  ? 


SOIL  EROSION  375 

5.  Give  effects  of  topography. 

0.   What  part  does  texture  of  soil  play  in  erosion? 

7.  How  does  the  vegetative  covering  atl'eet  erosion? 

8.  Why  should  the  character  of  rainfall  affect  erosion? 

U.  (Jive  Koine  idea  of  the  amount  of  material  moved  by  running  water. 
1U.   What  is  the  effect  of  this  deposit  in  many  instances?. 

11.  (Jive  effects  of  removal   of  surface  soil. 

12.  What  results  are  obtained  from  applying  plant  food  to  eroded  soil? 

13.  What  effect  does  erosion  have  on  the  physical  character  of  the  soil? 

14.  Define  sheet  erosion. 

1«).  How  does   it  reduce  productiveness? 

l(i.  What  benefits  are  derived    from   limestone  on  eroded  land? 

17.  What  are  good  meadow-  and  pasture-grasses? 

18.  What  are  good   legumes   for  hill   land  pastures? 
11).  What  are  the  uses  of  catch  crops? 

20.  What  use  may  be  made  of  crop  residues? 

21.  Tell  alxnil  the  amount  of  organic  matter  in  eroded  soils. 

22.  What  effect  does  it  have  that  causes  less  erosion  ? 

23.  What  are  the  advantages  of  deep  plowing? 

24.  What  are  the  advantages  of  contour  plowing  and  seeding? 
2;~>.  What  is  the  guide-row  terrace  and  what  are  its  advantages? 
2(i.  (Jive  advantages  of  the  level  bench  terrace. 

27.  Describe  the  Mangum  terrace. 

28.  (Jive  its  advantages. 

2!).   Discuss  reforesting  of  eroded  lands. 

.'50.  What  about  tile  as  a  method  for  preventing  erosion? 

31.  What  are   the   sources  of  gullies? 

32.  (Jive  methods  of  preventing  gullies. 

33.  Discuss  waterfalls.  Why  are  they  so  difficult  to  check? 

34.  How  may  dams  he  used  to  fill  gullies? 

35.  tJive  use  of  black  locust  on  gullied   land. 
30.  What  other  ways  of  filling  gullies? 

REFERENCES 

'Report  of  the  National  Conservation  Commission  ((10th  Congress.  Second 
(Session.  Senate  Document  <i~t>),  IDOll,  vol.  I,  p.  7!). 

J  Lcverett,  1<\,  Monograph  XXXVIII,  I'.  S.  (Jeol.  Survey. 

3  Mosier,  -J.  CJ.,  Circular  11!>.  Illinois  Station,  Washing  of  Soils  and  Methods 
of  Prevention  (Second  Kdition),  l!H2,  p.  7. 

*Soil  Report  No.  3,  Illinois  Station,  11)12,  p.  3. 

6  These  figures  are  drawn  from  Field  Operations  of  the  Htircau  of  Soils, 
U.  S.  1).  A.,  f>th  Report.  11)03.  The  average  figure  is  bused  on  reported 
analyses  of  (>3  samples  of  the  clay,  clay  loams,  silt  loams  and  loams 
of  the  Cecil,  DeKuIb,  Hagerstown,  and  Norfolk  Series. 

"Redding,  R.  J..  Cotton  Culture.  Bulletin  (13,  (Jeorgia  Station.  11)03.  p.  124. 

General  References. — MefJee,  \V.  J.,  Bulletin  71,  Bureau  of  Soils, 
T.  S.  I).  A..  11)11.  Ames,  C.  T.,  Bulletins  10S  and  lli:(.  Mississippi  Station. 
Report  of  Work  at  the  Holly  Springs  Branch  Station.  1!M)7-1!)14.  Illinois 
Soil  Reports,  No.  3.  11)12.  and  No.  11.  I'.M.V  Davis.  I!.  ().  K..  Bulletin  ISO. 
U.  S.  Department  of  Agriculture,  Soil  Krosion  in  the  South.  1015.  Callmun. 
F.  H.  II.,  Circular  20,  South  Carolina  Station,  (Jullving  and  it,s  Prevention, 
1913. 


CHAPTER  XXVIII 

ROTATION 

A  CROP  rotation  is  the  growing  of  two  or  more  crops  in  regular 
sequence  on  the  same  land.  Scientific  rotation  is  the  systematic 
growing  of  crops  on  the  same  soil  in  regular  succession  such  that 
each  crop  bears  a  useful  and  somewhat  vital  relation  to  some  or  all 
of  the  others  grown.  Rotation  is  very  closely  related  to  and  be- 
comes the  basis  of  soil  improvement.  The  object  of  a  rotation  is  to 
utilize,  to  the  very  best  advantage  in  the  production  of  maximum 
crops,  the  favorable  conditions  of  soil  with  respect  to  tilth,  moist- 
ure, temperature  and  food,  produced  by  other  crops,  and  to  elimi- 
nate any  unfavorable  conditions  produced  by  any  crop.  A  legume 
should  form  one  of  the  crops  of  the  rotation  because  of  its  value  in 
bringing  about  these  favorable  soil  conditions. 

Major  crops  in  rotations  are  the  main  crops  grown.  Minor  crops 
are  those  grown  for  catch,  cover,  or  green  manure  purposes. 

In  nature  no  very  distinct  rotation  of  plants  occurs  because 
the  same  thing  is  accomplished  in  a  measure  by  the  growing  to- 
gether of  different  plants  on  the  same  land.  Yet  we  see  that  nature 
has  its  own  system  of  rotation.  Certain  plants  may  grow  luxuri- 
antly for  a  few  years  and  then  be  almost  entirely  replaced  by  some 
more  favored  one.  Sweet  clover  has  be<en  observed  growing  along 
ditch  banks  for  several  years  and  then  has  been  crowded  out  by  some 
other  plant  without  any  apparent  cause.  As  a  result  of  weather 
conditions  some  weeds  are  very  abundant  for  a  year  or  two  and 
then  almost  entirely  disappear.  Fires  sometimes  aid  nature  in 
bringing  about  a  rotation  of  plants,  as  do  also  birds  and  other 
animals.  Any  natural  agency  of  seed  distribution  lends  its  assist- 
ance in  accomplishing  this  purpose. 

In  agricultural  practice  it  has  been  found  very  essential  to 
'rotate  crops.     The  object  of  farming  is  to  grow  crops  and  it  has 
been  found  in  general  farm  practice  and  determined  through  num- 
erous experiments  that  more  grain  and  other  crops  may  be  produced 
in  a  regular  rotation  than  by  growing  any  one  crop  year  after  year 
on  the  same  land. 
376 


ROTATION  377 

ADVANTAGES  OF  ROTATION 

1.  Better  Distribution  of  Work. — The  one-crop  system  throws 
a  large  amount  of  work  at  about  the  same  time  so  that  a  large 
force  of  men  and  horses  are  necessary  to  plant,  cultivate  or  harvest 
the  crop.     The  most  economical  use  of  time  and  labor  is  accom- 
plished when  it  is  more  uniformly  distributed  throughout  the  year. 
In  a  rotation  the  several  crops  are  planted  at  different  times.     They 
mature  so  as  to  distribute  the  work  of  harvesting  over  a  considerable 
period.    This  helps  solve  the  farmer's  labor  problems  by  furnishing 
more  permanent  employment  to  the  laborer. 

2.  Control  of  Insects  and  Plant  Diseases. — A  very  serious 
objection  to  any  one-crop  system  is  the  encouragement  it  gives  to 
injurious  insects  that  prey  upon  the  crop.     This  is  especially  true 
of  corn.    The  corn  root  aphis  and  the  corn  root  worm  become  very 
serious  pests  where  this  crop   is   grown   very   long  in   succession. 
Growing  some  other  crop  for  several  years  destroys  many  of  these. 
The  same  is  true  of  plant  diseases  such  as  flax  wilt,  cowpea  wilt, 
clover  sickness,  potato  scab,  dry  rot  of  corn,  etc.     These  are  worse 
than  the  insects.     They  may  be  completely  controlled  by  rotation, 
since  in  this  case  the  particular  host  plant  upon  which  each  lives 
will  not  be  present  every  year,  thus  creating  conditions  very  un- 
favorable for  their  survival. 

3.  Control  of  Weeds. — Many  crops  have  their  particular  weed 
or  weeds  that  are  in   some  way   favored   by  them.      Many   weeds 
favored  by  one  crop   will   be  smothered   by  another.     Cultivation 
of  one  crop  may  be  the  means  of  destroying  some,  while  others  may 
be  killed  by  pasturing  or  by  a  tough,  heavy  sod. 

One-crop  systems  tend  to  encourage  many  kinds  of  weeds.  At 
Hothamsted,  England,  on  the  plots  where  wheat  had  been  grown 
continuously  for  many  years  the  ground  became  so  foul  that  fallow- 
ing had  to  be  practiced  occasionally  to  eradicate  the  weeds.  Corn 
cockle  and  chess  growing  with  wheat  are  familiar  examples  in  this 
country.  Kemove  these  from  their  association  with  wheat  and  they 
are  easily  killed.  Old  pastures  sometimes  become  so  full  of  weeds 
that  the  grass  amounts  to  little.  Ox-eye  daisy,  yarrow,  verbena,  and 
iron  weed  sometimes  take  pastures.  Hence  it  becomes  as  necessary 
to  rotate  pastures  as  any  other  crop  unless  great  care  is  taken  to 
keep  these  enemies  out.  Pastures  and  meadows  may  be  kept  clean, 
as  seen  in  England,  where  the  grass  fields  are  several  decades  old. 


378  SOIL  PHYSICS  AND  MANAGEMENT 

These  are  the  exceptions.    England's  farms  are  models  of  scientific 
rotation. 

4.  Variation  in  Depth  of  Root  Systems. — By  rotation  differ- 
ent crops  with  root  systems  varying  in  depth  are  brought  succes- 
sively upon  the  land.     Some  especially  deep-rooting  crops,  such  as 
clovers  and  alfalfa,  should  be  grown.    These  obtain  much  of  their 
food  below  the  zone  from  which  the  ordinary  shallow-rooting  crops 
take  their  food.     More  than  this,  they  bring  much  plant  food  to 
where  it  may  be  reached  by  other  crops.    In  this  way  the  plant  food 
from  a  deeper  zone  is  utilized  and  soil  exhaustion  will  not  occur  so 
soon.    These  deep-rooting  crops  have  a  very  favorable  effect  in  open- 
ing up  the  subsoil  for  better  aeration  and  drainage. 

5.  Helps  Maintain  Good  Tilth. — At  the  University  of  Illinois 
one  plot  has  been  growing  corn  for  thirty -seven  years ;  another  has 
had  a  two-crop  system  of  corn  and  oats ;  a  third  has  had  a  three-crop 
system  of  corn,  oats,  and  clover  for  the  same  time.    The  soil  of  the 
first  is  compact,  "runs  together"  badly,  and  erodes  considerably. 
A  heavy  rain  packs  it  and  forms  a  smooth,  solid  surface.    The  second 
acts  somewhat  similarly  to  the  first  but  is  not  so  bad.    The  third  is 
mellow,  granular,  and  even  heavy  rains  do  not  cause  the  surface  to 
run  together.     This  difference  is  due  to  the  legume  crop  grown. 
No  crop  is  of  more  benefit  to  the  tilth  of  a  soil  than  a  deep-rooting 
legume. 

6.  Helps  to  Maintain  the  Organic  Matter. — The  part  rota- 
tion plays  in  maintaining  organic  matter  has  been  discussed  in 
Chapter  XI.     As  previously  shown,  a  legume  crop  is  essential  in 
every  scientific  rotation.    The  manner  in  which  the  legume  is  dis- 
posed of  is  of  the  utmost  importance.     Very  little  in  the  way  of 
permanent  improvement  is  accomplished  unless  the  legume  is  turned 
back  into  the  soil  either  directly  or  as  manure. 

7.  Rendering  Toxic  Substances  Less  Harmful. — Soils  some- 
times contain  organic  substances  that  are  harmful  to  plants.     The 
same  substance  is  not  equally  injurious  to  all  crops,  but  is  espe- 
cially detrimental  to  the  growth  of  the  kind  of  plants  that  gave  rise 
to  the  toxic  material.    Changing  the  crop  renders  this  less  harmful. 

8.  Produces  Larger  Yields. — From  what  has  been  said  it  will 
be  seen  that  rotated  crops  have  a  decided  advantage  over  those  of 
the  single-crop  system. 

Many  experiments  have  been  carried  on  at  different  stations 

that  prove  definitely  the  great  value  of  rotation  in  increased  yields. 

Iowa  gives  results  that  show  a  nine-year  average  for  continuous 


ROTATION 


379 


corn  of  51  bushels  per  acre  and  G4  bushels  for  corn  grown  in  a 
rotation  of  corn,  corn,  oats,  and  clover. 

Rotation  Compared  with  Continuous  Corn.    Ames,  Iowa 


1904 

1905 

I'.KX; 

1<>()7 

190S 

100!) 

1910 

mil 

1912 

Average 

Corn  in  rotation  of 
corn,     corn,    oats 
and  clover  

75 

87 

no 

57 

70 

54 

on 

44 

60 

64 

Continuous  corn  .... 

74 

73 

53 

47 

53 

31 

46 

32 

47 

51 

Jt  will  be  observed  that  the  yield  at  the  beginning  was  about  the 
same  for  each. 

At  the  Illinois  Station  corn  has  been  grown  for  thirty-seven 
years  in  comparison  with  a  corn  and  oats  and  a  corn,  oats,  and 
clover  rotation.  The  hist  four  crops  of  corresponding  years  average : 
Continuous  corn  2(5.4  bushels  per  acre,  corn  and  oats  rotation  34.6 
bushels,  and  the  corn,  oats,  and  clover  rotation  57.1  bushels. 

Yields  of  Corn,  When!  mid  Hay  Under  Dffircni  Systems  of  Cropping. 
Minnesota  Station  ' 


CJurn 

Wheat 

H 

»y 

Year 

Con- 

.'M'oar 

5-year 

Con- 

3-yrar 

5-yo.ir 

•l-yoar 

5-year 

tinu- 

rota- 

rota- 

tinu- 

rota- 

rota- 

rota- 

rota- 

ous 

tion 

tion 

ous 

tion 

tion 

tion 

tion 

Hushrl* 

Rnshrlx 

Ruxhrh 

Ruthrls 

niishrl* 

fill  Slid* 

Ton* 

Ton* 

1899 

20.X 

51.1 

31.3 

22.5 

25.3 

27.3 

19<X)  

37.5 

42.0 

5S.O 

14.5 

27.3 

25.0 

19<)1  

13.9 

42.0 

42.X 

10.0 

13.5 

1  5.2 

1.5X 

2.36 

1902  

* 

02.0 

7S.fi 

17.0 

18.1 

25.1 

2.25 

1.95 

903  

23.fi 

54.7 

X5.3 

10.3 

24.4 

30.X 

3.XO 

0.10 

904  

11.1 

45.1 

37.1 

20.X 

27.3 

32.0 

4.20 

5.77 

905  

25.1 

(5-1.  1 

MA 

20.X 

20.6 

30.9 

4.XO 

5.X  1 

9(Mi        .    .    . 

27  0 

30.1 

(>()  5 

14  1 

1  3  3 

22  0 

1  91 

3  IX 

907  

23.0 

35.2 

52.2 

24  5 

19  1 

23.!) 

1  .25 

1.42 

Average,  9  years  

22.9J 

4S.1 

50.7 

18.5 

21.0 

25.9 

2.X5t 

3.  SOJ 

Increase  

25.2 

33.8 

2.4 

7.4 

.95 

*  Record  lost. 


t  8  years. 


t  7  years. 


From  the  results  given  in  the  above  table  it  will  he  seen  that  con- 
tinuous cropping  has  a  greater  cfl'ect  <>M  corn  than  upon  wheat.  The 
.'•-year  rotation  increased  corn  •.'.">. •?  bushels,  while  the  increase  for 
wheat  was  only  '?.  I  bushels  per  acre. 

Ohio  has  been  carrying  on  some  experiments  for  about  10  years 
that  prove  the  value  of  rotations. 


380 


SOIL  PHYSICS  AND  MANAGEMENT 


Average  Annual   Yields  for  16  to  19   Years  When  Grown  Continuously  and 
Under  Three-  and  Five-year  Rotations.    Ohio  Station  * 


Rotation 

Corn 

Wheat 

Oata 

Clover 

Continuous                           .    . 

Bushels 

15.88 

Bushels 

7.52 

Bushels 

22.92 

Pounds 

3-year  rotation  

34.39 

10.63 

2,697 

5-year  rotation  

29.74 

10.21 

31.00 

2,267 

Increase  for  3-year  rotation 

18.51 

3.11 

8.08 

Rotation  gave  an  increase  of  18.5  bushels  per  acre  of  corn  and 
for  wheat  3.1  bushels,  showing  again  that  corn  responds  to  rotation 
better  than  wheat. 

PLANNING   A   ROTATION 

Planning  a  rotation  requires  a  great  deal  of  care  and  thought. 
It  should  be  made  not  for  the  present  alone  but  for  many  years  in 
the  future.  The  probable  effect  of  the  rotation  adopted  should  be 
studied  from  several  standpoints.  The  effect  on  the  fertility  and 
tilth  of  the  soil  should  receive  careful  attention.  Will  it  decrease 
or  increase  the  organic  matter  of  the  soil  is  a  question  that  should 
be  worked  out.  If  this  rotation  is  practiced,  what  will  be  the  condi- 
tion of  my  farm  after  fifty  years?  If  you  cannot  answer  this,  get 
the  knowledge  or  the  help  that  will  enable  you  to  do  so.  The  rota- 
tion would  depend  on  the  size  of  the  farm  to  some  extent.  That 
for  one  of  sixty  acres  would  not  apply  to  a  four  hundred-acre  farm. 
The  rotation  should  vary  with  the  character  of  the  soil.  A  rotation 
for  a  heavy,  rich,  black  soil  certainly  would  not  be  fitted  for  a  sandy 
soil,  or  vice  versa.  Soils  low  in  organic  matter  should  have  a  system 
of  rotation  whose  object  is  to  build  up  the  soil  in  this  particular. 
Acid  soils  will  grow  different  crops  than  soils  containing  limestone. 
The  maintenance  of  the  fertility  and  tilth  of  the  soil  should  be  a 
very  important  factor  in  determining  the  rotation. 

The  system  of  farming  to  be  practiced  should  be  one  of  the  con- 
trolling factors  in  determining  the  crops  grown.  A  fruit-grower, 
a  dairyman,  a  grain  farmer,  or  a  stock-raiser  would  each  follow  dif- 
ferent systems.  In  any  system  the  value  of  the  crops,  both  those  to 
be  used  on  the  farm  and  those  to  be  sold,  must  be  considered  in  their 
selection,  since  the  returns  from  the  crop  and  its  relation  to  other 
crops  is  the  thing  that  should  determine  its  use  in  the  rotation. 
The  most  profitable  crop  should  have  the  most  favorable  place  in  the 
rotation.  In  the  corn  and  wheat  belt  these  should  have  this  place, 


ROTATION  381 

aiid  likewise  of  the  other  great  money  crops,  such  as  cotton,  tobacco, 
potatoes  and  others. 

As  a  general  rule  a  rotation  of  three  to  live  years  is  more  desira- 
ble than  a  longer  one.  The  short  cycle  requires  less  trouble  and  time 
to  get  it  started  and  is  easier  to  maintain  when  once  under  way. 
If  a  crop  fails  in  a  three-  or  four-year  cycle  it  is  not  difficult  to 
maintain  the  rotation,  while  if  a  failure  occurs  in  a  longer  cycle  it 
may  disarrange  the  system  to  a  greater  or  less  extent. 

Because  of  the  rearrangement  of  fields  and  the  adjustment  of 
crops,  it  is  rather  difficult  to  get  a  rotation  under  way,  usually  re- 
quiring several  years,  and  it  is  almost  equally  difficult  to  change  it 
after  once  it  is  started.  The  rotation  should  be  maintained  even 
if  a  crop  does  fail.  A  substitute  crop  should  be  planned  to  take  the 
place  of  those  crops  that  are  liable  to  fail.  This  will  not  be  needed 
very  often. 

The  farm  should  be  divided  into  as  many  fields  as  there  are 
years  in  the  rotation  and  the  crops  grown  in  regular  succession  on 
these  fields.  On  large  farms  the  rotation  may  be  duplicated.  There 
should  be  at  least  one  legume  crop,  preferably  a  biennial  or  peren- 
nial, and  not  more  than  two  tilled  crops,  during  the  cycle,  the 
number  depending  upon  the  soil,  as  these  cause  considerable  loss  of 
organic  matter. 

Places  in  Rotations  for  Crops. — Corn  succeeds  well  after 
clovers,  alfalfa  and  pasture  and  docs  fairly  well  after  wheat  and 
oats,  especially  for  fall  plowing.  Jn  sod  ground  two  or  three  crops 
of  corn  may  be  grown  successfully,  but  more  than  two  in  succession 
on  ordinary  soil  are  not  deemed  best. 

Wheat  does  not  follow  corn  well  even  if  the  latter  matures  sev- 
eral weeks  before  seeding  time.  Wheat  does  well  after  potatoes, 
clover,  alfalfa,  pasture  or  soybeans,  the  only  danger  being  its  liability 
to  lodge  caused  by  the  excess  of  available  plant  food,  especially 
nitrogen.  Oats  is  a  good  crop  to  precede  wheat  if  the  plowing  is 
done  early.  Wheat  follows  wheat  very  well,  but  there  is  too  much 
danger  from  Hessian  fly  in  some  latitudes. 

Oats  is  a  crop  that  is  adapted  to  the  cooler  part  of  the  temperate 
zone.  South  of  this  the  ordinary  spring-sown  oats  encounter  the 
hot  weather  at  filling  time,  so  that  a  partial  failure  may  result.  In 
the  South  winter  oats  are  grown  to  soine  extent  with  fair  success. 
There  is  a  belt,  between  these  where  neither  fall  nor  spring  oats 
do  well.  The  summers  are  too  hot  for  the  spring  seeding  and  the 
winters  too  cold  for  the  fall  oats. 


382  SOIL  PHYSICS  AND  MANAGEMENT 

In  the  corn  and  wheat  belt  and  corresponding  latitudes  oats  are 
almost  universally  seeded  after  corn.  Even  in  the  southern  states 
this  is  practiced.  If  they  should  follow  clover  or  potatoes,  lodging  of 
the  crop  would  almost  certainly  occur,  with  consequent  loss.  They 
will  follow  wheat,  millet  or  cotton  well. 

Barley  does  well  in  the  southern  oats  helt  and  under  practically 
the  same  conditions.  It  may  follow  wheat,  oats  or  corn. 

Rye  may  be  grown  under  practically  the  same  climatic  conditions 
as  wheat,  but  it  is  a  better  forager  and  produces  more  on  poorer 
soils.  In  the  middle  west  it  is  a  common  crop  for  very  sandy  lands. 

The  clovers  are  almost  universally  seeded  with  wheat,  oats  or 
barley  as  nurse  crops.  Occasionally  they  may  be  seeded  in  corn  or 
cotton  after  the  last  cultivation,  but  the  catch  is  uncertain. 

Soybeans  and  cowpeas  follow  almost  any  crop,  but  there  is  noth- 
ing gained  by  having  these  succeed  other  legume  crops.  A  non- 
leguminous  crop  should  intervene  or  at  least  be  grown  in  conjunc- 
tion with  one  of  the  legumes. 


SOME  PRACTICAL  ROTATIONS 

1.  For  the  Corn  and  Winter  Wheat  Belt. — In  this  belt  corn 
and  wheat  are  the  money  crops,  and  they  should  be  given  the  most 
favorable  places  in  the  rotation.  If  any  crop  is  grown  that  is  of 
special  benefit  to  the  soil,  these  should  have  the  advantage  of  its 
effect.  The  best  place  for  corn  is  following  the  legume.  If  two 
important  money  crops  are  placed  in  the  rotation,  each  should  be 
given  the  best  place  possible.  This  belt  is  characterized  by  hot 
summers  and  cold  winters,  with  the  annual  rainfall  varying  from 
20  to  48  inches.  Corn,  wheat,  oats,  and  rye  are  the  principal 
cereals  (Fig.  189). 

A  short-cycle  rotation  that  is  sometimes  practiced  is :  first  year, 
corn;  second  year,  oats,  seeded  to  clover;  and  third  year,  clover. 
This  is  a  good  rotation  to  maintain  organic  matter,  but  it  is  not  as 
profitable  as  some  others. 

An  excellent  four-year  rotation  is  made  by  adding  another  year 
of  corn  to  the  former,  making  (1)  corn;  (2)  corn;  (3)  oats 
(clover)  ;  and  (4)  clover.  This  exhausts  the  soil  more  rapidly  than 
the  former  and  is  best  adapted  to  fertile  soils-  well  supplied  with  or- 
ganic matter.  If  it  is  desired  to  grow  wheat,  a  four-year  rotation 
is  as  follows:  (1)  corn,  (2)  oats,  (3)  wheat  (clover),  (4)  clover. 
This  is  well  adapted  to  a  rich  soil  such  as  black  clay  loam  or  a 


383 


384  SOIL  PHYSICS  AND  MANAGEMENT 

heavy  phase  of  brown  silt  loam.  If  two  crops  of  wheat  are  desired 
in  the  rotation,  the  extra  one  may  follow  the  clover,  seeded  again  to 
a  different  kind  of  clover  to  be  plowed  under  for  corn.  This  changes 
it  to  a  five-year  cycle.  Another  practical  one  where  wheat  is  the 
leading  crop  is  (1)  wheat;  (2)  wheat  (clover)  ;  and  (3)  clover. 

Probably  one  of  the  best  four-year  rotations  for  the  corn  belt 
and  one  which  gives  two  good  money  crops  advantageously  located 
in  the  cycle  is  (1)  corn,  (2)  oats  (clover),  (3)  clover;  (4)  wheat 
(clover).  This  gives  three  years  during  which  the  legume  crops 
are  growing  and  the  rotation  is  adapted  to  soils  deficient  in  nitrogen 
and  low  in  organic  matter.  On  the  grain  farm  practically  all  of 
the  clover  crop  should  be  turned  back  into  the  soil  in  any  of  these 
rotations.  The  clover  may  be  clipped  and  left  on  the  land  and  the 
second  crop  may  be  harvested  for  seed  and  the  straw  returned  to  the 
soil.  All  crop  residues  not  fed  should  be  turned  back  into  the  soil. 
If  more  corn  is  desired  this  may  be  changed  to  a  five-year  rotation 
by  adding  another  year  of  corn,  making  (1)  corn,  (2)  corn,  (3) 
oats  (clover),  (4)  clover,  and  (5)  wheat  (clover). 

These  rotations  are  well  adapted  to  either  grain  or  mixed  farm- 
ing, since  the  clover  may  be  pastured  to  good  advantage.  Another 
year  of  pasture  or  hay  may  be  easily  added  by  seeding  clover  and 
timothy  instead  of  clover  alone.  The  first  year  of  these  the  crop  will 
be  largely  clover,  while  the  second  will  be  mostly  timothy.  If  the 
clover  should  fail,  soybeans  may  be  substituted  to  be  cut  for  hay  or 
seed.  Soybean  straw  is  eaten  very  readily  by  stock. 

If  soybeans  or  cowpeas  can  be  used  to  good  advantage,  a  rotation 
containing  one  of  the  crops  may  well  be  practiced.  The  rotation 
might  be  (1)  corn,  (2)  cowpeas  or  soybeans,  (3)  wheat  (clover), 
(4)  clover.  The  cowpea  or  soybean  hay  may  be  fed1  to  stock  and 
the  manure  returned  to  the  soil. 

Alfalfa  may  be  included  in  the  rotation  by  adding  another  field 
and  growing  it  while  the  other  crops  are  going  the  rounds  of  the 
regular  rotation.  At  the  end  of  this  cycle,  the  alfalfa  field  is  then 
put  into  corn  and  the  clover  field  is  seeded  to  alfalfa. 

In  these  rotations  alsike,  mammoth,  medium  red,  or  sweet  clover 
may  be  used.  Where  conditions  are  very  favorable  for  getting  a 
catch  of  alfalfa,  this  crop  may  be  substituted  for  clover,  but  as  a 
general  rule  it  is  a  wise  plan  to  leave  a  good  stand  of  alfalfa  for 
several  years  when  once  obtained. 

2.  For  the  Cotton  Belt. — This  region  possesses  many  advan- 
tages in  climate  over  the  corn  belt.  It  has  a  larger  and  better  dig- 


ROTATION  385 

tributed  rainfall  with  a  longer  growing  season  and  mild  winters. 
The  unusual  facilities  for  growing  a  money  and  a  soil  renovating 
crop  during  the  same  season  give  this  section  decided  advantages 
over  the  corn  belt.  Winter  cover  crops  on  rolling  land  for  prevent- 
ing erosion,  as  well  as  green  manure  crops  for  increasing  the  scanty 
supply  of  organic  matter,  should  be  grown  more  extensively. 

The  principal  money  crop  is  cotton,  yet  a  great  many  special 
crops  are  grown  in  different  states.  Mixed  farming  predominates 
in  many  places.  In  Kentucky,  Tennessee,  and  Oklahoma  livestock 
farming  prevails,  with  the  growing  of  grains  next  in  importance.  In 
Texas  and  Arkansas  livestock  is  first,  with  cotton  production  second. 
Cotton  is  the  leading  crop  in  Alabama,  Mississippi,  Georgia,  South 
Carolina,  and  Louisiana.  In  the  latter,  sugar  cane  is  next  in  im- 
portance. This  is  also  grown  in  Xorth  and  South  Carolina. 
Tobacco  is  grown  extensively  in  Maryland,  Virginia,  Kentucky  and 
Xorth  Carolina.  Truck  crops  and  fruits  are  extensively  grown  in 
Florida  and  near  the  Gulf  in  other  states.  Corn,  rice,  wheat,  oats, 
kafir  corn,  milo  maize,  rye  and  buckwheat  are  grown  in  different 
parts  of  the  region. 

The  forage  crops  are  varied  and  comprise  alfalfa,  cowpeas,  soy- 
beans, red,  alsike,  crimson,  Japan,  and  sweet  clovers,  vetches, 
timothy,  blue,  Johnson,  brome,  and  Bermuda  grasses,  and  millet. 
Peanuts,  hemp,  Irish  and  sweet  potatoes  are  special  crops  in  some 
sections. 

This  shows  the  large  number  of  crops  that  are  grown  in  this  belt 
and  the  great  opportunity  for  rotation.  Much  of  the  soil  is  acid 
and  deficient  in  organic  matter  and  nitrogen,  and  the  rotation 
should  be  planned  to  maintain  or  increase  the  nitrogen  rather  than 
attempt  to  supply  it  from  commercial  fertilixers.  legumes  must 
be  grown  that  are  not  affected  by  acid  unless  limestone  or  lime  has 
been  applied  to  the  soil.  Japan  clover,  cowpeas,  and  soybeans  fill 
these  conditions,  since  they  do  very  well  on  acid  soils. 

The  cotton  belt  includes  a  very  extensive  area,  large  numbers 
of  widely  different  soils,  and  considerable  variation  in  altitude. 
These  tend  to  give  variety  to  the  crops  grown.  The  rotation  for  this 
belt,  should  have  one  or  more  money  crops,  such  as  potatoes,  cotton, 
tobacco,  sugar  cane,  wheat,  rice,  one  or  more  for  feed  and  a  crop 
for  soil  improvement.  A  very  good  rotation  is  (1)  corn  (cowpeas). 
('.?)  winter  oats  (cowpeas),  (3)  cotton  (plover). 

Where  tobacco  is  grown,  the  following  may  be  practiced:   (1) 
tobacco,  (2)  whoat  (clover),  and  (•'?)  clover:  or  (1)  corn  (cowpeas), 
25 


386  SOIL  PHYSICS  AND  MANAGEMENT 

(2)  tobacco,  (3)  wheat  (clover)  and  (4)  clover.  In  the  rice 
district  the  following  is  recommended:  (1)  rice,  (2)  rice,  (3)  corn 
(cowpeas),  (4)  winter  oats  (cowpeas),  or  (4)  winter  oats  and 
vetch  (cowpeas). 

If  one  of  the  money  crops  is  potatoes,  then  (1)  corn  (cow- 
peas),  (2)  potatoes  (soybeans),  and  (3)  cotton  (crimson  clover) 
may  form  the  rotation.  The  legumes  in  corn  and  cotton  should 
be  used  primarily  for  soil  improvement,  while  those  following  other 
crops  may  be  used  for  hay  or  soil  improvement.  These  rotations 
are  only  suggestive.  For  the  stock  farm,  almost  any  of  the  above 
rotations  may  be  extended  two  or  three  years  for  hay  or  pasture,  or 
both,  with  whatever  meadow  or  pasture  grass  does  best  in  the 
locality,  whether  it  is  redtop,  timothy,  brome,  blue,  or  Bermuda 
grass. 

3.  For  Hay  and  Pasture  Province. — The  hay  and  pasture 
province  (Fig.  189)  occupies  the  northeastern  part  of  the  United 
States  in  the  cooler  temperate  zone  with  a  southward  extension 
m  the  Appalachian  Mountains  to  northern  Georgia.    Grass  for  hay 
and  pasture  is  the  principal  crop  grown,  yet  corn,  potatoes,  rye, 
oats,  wheat,  clover,  and  barley  are  somewhat  extensively  produced 
in  many  areas. 

The  short  seasons  do  not  permit  the  growing  of  two  crops  and 
hence  the  greater  difficulty  of  raising  soil-renovating  crops.  There 
is,  however,  this  advantage,  that  oxidation  of  organic  matter  does 
not  take  place  so  rapidly  as  in  warmer  climates  and  the  supply  is 
therefore  easier  to  maintain. 

The  following  rotations  are  recommended:  (1)  Potatoes,  (2) 
rye  (clover),  (3)  clover;  or  (1)  corn,  (2)  potatoes,  (3)  rye 
(clover),  (4)  clover.  For  pasture  or  hay  timothy  may  be  seeded 
with  the  clover  and  left  for  two  or  three  years.  If  desirable,  oats 
may  be  substituted  for  rye.  If  potatoes  are  omitted,  a  good  rotation 
is  as  follows:  (1)  corn,  (2)  oats,  (3)  wheat  (clover),  (4)  clover 
and  timothy,  (5)  timothy.  This  rotation  may  be  shortened  by 
leaving  out  wheat,  making  a  very  desirable  rotation  for  some 
localities. 

4.  The  spring  wheat  region  and  the  great  plains  province 
occur  east  of  the  Rocky  Mountains,  and  wheat  is  the  principal  crop 
of  both.    In  the  former  (1)  corn,  (2)  wheat,  (3)  wheat,  and  (4) 
legume  may  be  practiced.    In  some  localities  potatoes  may  be  sub- 
stituted for  corn.     In  a  live  stock  system,  clover  and  timothy  may 
be  sown  and  used  for  hay  and  pasture. 


ROTATION  387 

The  crops  of  the  great  plains  province  vary  extensively.  Besides 
wheat,  the  sorghums  form  a  very  valuable  crop  in  the  southern 
third.  To  the  north  of  this,  wheat,  together  with  some  corn  and 
alfalfa,  is  the  principal  crop.  No  definite  rotation  has  been  worked 
out  for  this  area. 

The  principal  farm  crops  in  the  provinces  west  of  the  Rocky 
Mountains  are  wheat  and  alfalfa,  with  some  corn,  oats,  barley,  rye, 
and  sugar  beets.  The  need  of  soil  improvement  is  not  so  evident 
here  as  in  humid  regions,  because  of  a  much  greater  original  sup- 
ply of  plant  food.  The  extensive  growth  of  alfalfa  furnishes  a 
ready  and  effective  means  for  building  up  the  soil. 

QUESTIONS 

1.  Define  a  rotation  of  crops. 

2.  How  does  a  scientific  rotation  differ  from  tlie  above? 

3.  (Jive  the  objects  of  a  rotation. 

4.  What  are  major  crops  ? 

5.  What  are  minor  crops? 

6.  How  are  crops  rotated  in  nature? 

7.  What  is  the  primary  object  of  farming? 

8.  How  does  rotation  affect  the  distribution  of  work? 

!•.  Why  is  a  one-crop  system  favorable  to  the  development  of  insects? 

10.  Can   you  give  an   instance  of   disease    caused   by   continuous   cropping? 

11.  How  does  rotation  prevent  disease? 

12.  How  are   weeds   kept  down    by    rotation? 

13.  Give  some  examples  of  troublesome  weeds  in  your  locality  that  may  be 

kept  down   by  rotation. 

14.  Why    is    it    a    good    practice    to    grow    crops    that    root    at    different 

depths? 

15.  What  part  does  rotation  play  in  maintaining  tilth? 

10.  What  are  toxic  substances  and  how  does   rotation  affect  these? 

17.  (Jive   the    results   obtained    at    the    Iowa   Station   for    continuous   corn 

and  rotation. 

18.  What  results  were  obtained  at  the  Illinois  Station? 

1!).  What  do  the  Minnesota  experiments  show  in  regard  to  corn?     Wheat? 

Hay? 

•20.  Which  cereal  responds  best  to  rotation? 
'21.  If  corn  is  worth  50  cents  and  wheat  $1.05  per  bushel  and  hay  $S  per 

ton,  what  is  the   total   value  of  the  average  crops   in  a  three-year 

rotation?     In  a  live-vear  rotation? 

22.  Which   rotation  gave  the  greatest  acre  value  for  the  crop?      (Assume 

that  in  a  five-year  rotation,  three  crops  of  hay  were  grown.) 

23.  Give  a  synopsis  of  the  Ohio  results. 

•24.  What  tilings  are  to  be  considered  in  planning  a  rotation? 

•25.  What  importance  should  l>e  placed  on  the  soil  in  these  plans? 

'2<>.  What  consideration   should  guide  in  the  selection  of  crops? 

'27.  What  determines  the  succession  of  crops? 

'2H.  What  about  the  length  of  the  rotation? 

•2!>.  Why  is  it  difficult  to  get  a  rotation  under  way? 

30.  Why   is  it  advisable  to  divide  the  farm  into  as  many   fields  aa  there 
are  crop?  in  the  rotation? 


388  SOIL  PHYSICS  AND  MANAGEMENT 

31.  Where  should  corn  be  placed  in  the  rotation? 

32.  Where  is  the  best  place  for  wheat? 

33.  Where  are  oats  grown  best? 

34.  Where  are  winter  oats  grown? 

35.  What  crops  may  well  be  followed  by  oats? 

36.  Where  may  rye  be  seeded  ? 

37.  What  is  a  nurse  crop  and  why  necessary? 

38.  What  do  cowpeas  and  soybeans  follow? 

39.  Locate  the  corn  and  winter  wheat  belt. 

40.  What  are  the  principal  crops  there  ? 

41.  Give  a  good  short-cycle  rotation. 

42.  Give  a  good  four-year  rotation. 

43.  What  is  the  rotation  if  two  crops  of  wheat  are  desired? 

44.  Give  a  four-year  rotation  in   which   legumes  are  grown   three   out  of 

four  years. 

45.  How  may  these  be  adapted  to  mixed  farming? 

46.  What  is  to  be  done  if  clover  should  fail? 

47.  What  is  the  place  of  soybeans  or  cowpeas  in  the  rotation? 

48.  How  may  alfalfa  be  included  in  the  rotation? 

49.  Locate  the  cotton  belt. 

50.  What  advantages  over  the  corn  and  winter  wheat  belt  does  it  possess? 

51.  What  are  the  principal  money  crops? 

52.  Name  some  other  crops  grown  in  this  belt. 

53.  Give  the  forage  crops  grown. 

54.  Give  a  practical  rotation  with  tobacco,  cotton,  rice  and  potatoes. 

55.  What  should  be  done  with  the  legumes? 

56.  How  may  these  be  adapted  to  livestock  farming? 

57.  Where  is  the  hay  and  pasture  province? 

58.  What  are  its  advantages  and  disadvantages? 

59.  Give  rotations  that  may  be  practiced. 

60.  Locate  the  spring  wheat  region. 

61.  Name  the  crops  and  give  a  rotation. 

62.  What  are  the  crops  of  the  great  plains  region  ? 

63.  What   are   the   important   crops   of    the    province    west   of   the   Rocky 

Mountains  ? 

REFERENCES 

1Hays,   W.   M.,   Boss,   Andrew,   Wilson,   A.    D.,   and    Cooper,   Thomas   P., 

Bulletin  125,  Minnesota  Station,  1912,  p.  36. 
'Circular  131,  Ohio  Station. 

General  References. — Carleton,  M.  A.,  Small  Grains,  1916.  Liv- 
ingston, George,  Field  Crop  Production,  1915.  Montgomery,  E.  G.,  Pro- 
ductive Farm  Crops,  1915.  Piper,  C.  V.,  Forage  Plants.  1914.  Duggar, 
J.  F.,  Southern  Field  Crops,  1915.  Parker,  E.  C.,  Field  Management  and 
Crop  Rotation,  1915. 


APPENDIX    I 

SOIL  FERTILITY 

WITHOUT  attempting  to  go  into  the  subject  of  soil  fertility  to 
any  great  extent,  the  authors  have  thought  that  a  brief  discussion 
of  the  subject,  giving  some  of  the  underlying  principles,  would  be 
helpful  to  the  farmer.  The  field  is  such  a  large  one,  and  the  theories 
advanced  are  so  varied  and  conflicting,  that  the  practical  farmer 
is  at  a  loss  to  know  what  to  do,  and  as  a  consequence  does  nothing. 
The  fertility  needs  of  soils  may  be  determined  in  three  ways:  (1) 
by  chemical  analysis,  by  which  the  amount  of  plant  food  may  be 
determined,  (2)  by  pot  culture  experiments  in  greenhouses  under 
almost  perfect  conditions,  and  (3)  by  actual  field  tests,  where  plant 
foods  of  different  kinds  may  be  applied  and  the  results  compared 
with  those  of  an  equal  area  of  the  untreated  soil  growing  the  same 
crop. 

Permanent  Agriculture. — Agriculture  is  usually  considered  a 
permanent  industry,  but  it  is  no  more  permanent  than  the  natural 
soil  itself.  If  the  fertility  of  the  natural  soil  is  inexhaustible,  then 
agriculture  is  a  fixed  industry  and  likewise  those  industries,  com- 
merce, manufacturing,  and  mining,  which  depend  so  largely  upon 
agriculture.  If  history  tells  us  anything  about  agriculture  it  is 
this:  that  it  is  not  permanent,  that  nations  have  fallen  because  the 
agriculture  upon  which  their  civilization  depended  had  failed. 

Are  Soils  Inexhaustible? — The  productiveness  of  soils  depends 
upon  the  amounts  and  kinds  of  plant  food  elements  they  contain, 
the  favorable  conditions  for  plant  growth  that  they  offer,  and  the 
friendly  bacteria  present.  Chemical  analyses  show  that  plants 
contain  certain  mineral  elements  which  they  obtain  from  the  soil. 
Analyses  show  further  that  soils  contain  these  elements  in  limited 
quantities,  and  it  requires  no  great  amount  of  mathematical  knowl- 
edge to  see  that  if  plants  take  even  small  amounts  of  these  elements 
from  this  limited  supply,  reduction  and  final  exhaustion  are  sure 
to  follow  unless  the  necessary  elements  are  added  by  the  farmer. 

Complete  exhaustion  of  plant  food  is  not  necessary  to  render  a 
soil  unproductive.  If  the  soil  presents  adverse  conditions  to  the 
plant,  either  through  lack  or  excess  of  water,  poor  aeration,  or  bad 
physical  condition,  or  if  the  proper  bacteria  are  not  present,  or, 

389 


390 


SOIL  PHYSICS  AND  MANAGEMENT 


being  present,  are  not  under  favorable  conditions  for  carrying  on 
their  work,  the  plant  suffers  and  the  soil  appears  as  if  exhausted. 

Plant  Food  Elements. — Ten  elements  are  essential  to  the 
growth  of  plants.  (See  the  table  on  page  2.)  Of  these,  sulphur, 
calcium,  magnesium,  iron,  nitrogen,  phosphorus,  and  potassium  are 
furnished  by  the  soil.  The  last  three  are  the  ones  most  liable  to  be 

Plant  Food  in  Crops  * 


Crop 

Kind 

.Amount 

gen 

phorus 

slum 

Mag- 
nesium 

cium 

Wheat  

grain 

50  bushels 

Pounds 

71 

Pounds 

12 

Pounds 

13 

Pounds 

4 

Pound* 
1 

Corn  

straw 
grain 
stover 

2}4  tons 
100  bushels 
3  tons 

25 
100 

48 

4 
17 
6 

45 
19 
52 

4 

7 
10 

10 

1 

21 

cobs 

V£  ton 

2 

2 

Rve 

grain 

40  bushels 

38.1 

8.3 

11.2 

2.6 

0.9 

Oats  

straw 
grain 

2l/z  tons 
100  bushels 

25 
66 

6.5 
11 

35 
16 

3.5 
4 

11.0 
2 

Barley  

straw 
grain 

2^2  tons 
50  bushels 

31 
42 

5 
7.9 

52 
10.1 

7 
2.9 

15 
1.0 

Clover  

straw 
seed 

2600  pounds 
4  bushels 

15.O 

7 

2.  A 
2 

J3.7 
3 

.0 

1 

o.U 
1 

hay 
lint 

4  tons 
1000  pounds 

160 
3 

20 
0.4 

120 
4 

ol 

Cotton  

seed 

2000  pounds 

63 

11 

19 

Soy  beans  

stalk 
seed 

4000  pounds 
25  bushels 

O  oc  inns 

102 
80 
7Q 

18 
13 

0 

59 
24 

4Q 

2.1 

'  '  1.7 

3  tons 

130 

14 

98 

Tobacco      < 

deaf 

1800  pounds 

72 

3.5 

90 

11.7 
n  o 

67.5 

Timothy  hay 

[  stalk 

3200  pounds 
3  tons 

llo.4 
72 

.5 
9 

llo.4 
71 

u.y 
2.4 

ZoA 

7.2 

Alfalfa  hay  

6  tons 

300 

27 

144 

22.8 

218.4 

Sugar  beets  

20  tons 

100 

18 

157 

72 

64 

Potatoes         

300  bushels 

63 

13 

90 

5.4 

3.6 

Turnip-roots  

15  tons 

75.1 

12 

111 

54 

183 

Turnip-leaves  

2  tons 

16 

2 

18.4 

11.2 

109.2 

Fat  cattle 

1000  pounds 

25 

7 

1 

Milk 

10000  pounds 

57 

7 

12 

*  Compiled  from  various  sources. 


deficient  in  soils.  There  are  many  indications,  however,  that  cal- 
cium may  become  so  low  that  legumes,  which  require  large  amounts 
of  it,  may  suffer  in  their  growth  because  of  an  insufficient  supply. 

Removal  of  Plant  Food. — Crop  Requirements. — Removal  of 
plant  food  from  the  soil  by  the  crop  is  one  of  the  common  causes 


SOIL  FERTILITY  391 

of  lessened  production.  From  the  table  on  page  390,  which  gives 
the  amount  of  plant  food  used  by  some  common  crops,  it  will  be 
seen  that  a  fifty-bushel  crop  of  wheat  requires  ninety-six  pounds  of 
nitrogen,  sixteen  of  phosphorus,  fifty-eight  of  potassium,  eight  of 
magnesium,  and  eleven  of  calcium,  a  total  of  only  one  hundred  and 
seventy-nine  pounds.  This  is  only  two  and  one-fourth  per  cent  of 
the  weight  of  grain  and  straw  produced.  The  percentage  of  plant 
food  taken  from  the  soil  is  the  same  for  corn,  while  for  oats  it  is 
slightly  more  than  two  and  one-half  per  cent.  For  the  crop  to 
obtain  even  this  small  amount,  it  is  necessary  that  much  larger 
amounts  be  present  in  the  soil,  since  only  a  small  proportion  is 
available  each  season.  The  yields  given  in  the  preceding  table  are 
high,  but  no  larger  than  rich  soils  will  produce  under  favorable 
conditions. 

The  legumes  take  most  of  their  nitrogen  from  the  air,  but  the 
other  elements  given  in  the  table  are  taken  from  the  soil.  Other 
crops  take  all  of  their  supply  of  these  elements  from  the  soil.  Be- 
sides the  elements  given  in  the  preceding  table,  iron  is  taken  from 
the  soil.  However,  there  is  such  an  abundance  of  iron  in  the  soil 
and  plants  require  so  little  that  soils  probably  will  never  become 
deficient.  In  the  case  of  sulphur,  the  amount  needed  is  small  and 
the  soil  receives  some  from  the  air  during  rains. 

Supply  of  Plant  Food  in  Soils. — The  supply  of  plant  food  de- 
pends upon  several  factors.  Probably  the  most  important  is  the 
rock  from  which  the  soil  was  derived.  A  soil  derived  from  a  sand- 
stone may  contain  very  little  plant  food  of  any  kind.  A  granitic 
soil  will  probably  contain  large  amounts  of  calcium,  potassium, 
some  magnesium,  and  phosphorus.  A  limestone  soil  would  contain 
considerable  amounts  of  each  element.  Soils  formed  by  mixtures 
of  various  rocks  usually  contain  the  largest  supply. 

Nitrogen  is  nearly  always  a  later  acquisition.  Very  few  rocks, 
as  that  term  is  commonly  used,  contain  nitrogen. 

Leaching  removes  large  amounts  of  plant  food,  and  for  this 
reason  the  soils  of  humid  regions  contain  less  than  those  of  arid 
ones.  Some  exceptions  occur  in  swamps,  where  the  mineral  plant 
food  has  been  carried  in  by  washing  and  leaching  from  the  higher 
areas.  Conditions  are  favorable  for  the  accumulation  of  nitrogen 
through  the  more  luxuriant  growth  and  less  rapid  oxidation  of  vege- 
tation. The  physical  composition  of  the  soil  plays  a  very  important 
part  in  leaching,  since  the  smaller  the  soil  particles  the  less  the 
leaching. 


392 


SOIL  PHYSICS  AND  MANAGEMENT 


The  cropping  to  which  the  soil  has  been  subjected  determines 
to  a  large  extent  the  plant-food  content.  Every  crop  removed  from 
the  land  takes  away  a  certain  amount  of  food,  thus  slowly  reducing 
the  supply. 

The  next  table  gives  the  amount  of  plant  food  in  soils  from 
various  countries. 

Total  Plant  Food  in  Some  Residual  Soils.* — Pounds  in  Two  Million  Pounds 

of  Soil 


Sulphur 

Phos- 
phorus 

Potas- 
sium 

Calcium 

Mag- 
nesium 

Maryland  barrens  

180 

2000 

580 

840 

Adobe  soil,  New  Mexico  

5200 

8200 

28600 

198800 

35600 

Coral  limestone,  Bermuda  Islands. 
Soil  from  gneiss  

isso 

5400 
740 

2000 
22200 

50200 
5600 

5800 
7000 

Soil  from  gabbro  

740 

720 

15400 

7800 

10600 

Serpentine  soil        

560 

1140 

27600 

8200 

39000 

Cambrian  sandstone  soil  .    .    . 

800 

1240 

57400 

9000 

14800 

Trenton  limestone  soil  

820 

1340 

51600 

8200 

10400 

*  Compiled  from  various  sources. 

Fertility  in  Russian  Steppe  or  Tchernozem  Soils.1 — Pounds  in  Two  Million 

Pounds  of  Soil 


Nitrogen 

Sulphur 

Phos- 
phorus 

Potas- 

-• 

Calcium 

Mag- 
nesium 

Vir°in 

5400 

560 

1220 

11950 

21562 

8800 

Cultivated  

4800 

640 

1133 

8630 

18700 

9000 

Plant  Food  in  Missouri  Soils.2 — Pounds  in  Two  Million  Pounds  of  Soil 


Soil 

Total 
nitrogen 

Acid 
soluble 
phosphorus 

Acid 
soluble 
potassium 

The  standard  of  a  very  fertile  soil          

6000 

2000 

5300 

Northeast  Missouri  level  prairie  (Vandalia)  .  .  . 
Northeast  Missouri  level  prairie  (High  Hill)..  . 
Northeast  Missouri  rolling  prairie  (Hurdland)  . 
Northeast  Missouri  rolling  prairie  (Fulton)..  .  . 
North  Missouri  timber  soil  (Laclede)   

3640 
2700 
3760 
3640 
3000 

1918 
1608 
1978 
1754 
1221 

6175 
4714 
6089 
7188 
5362 

Ozark  upland  (Climax  Springs)  

1180 

800 

"SS'.t 

Ozark  upland  (Otterville)               

1820 

1350 

4117 

Ozark  upland  (Stonehill)       

1620 

740 

2623 

Ozark  border  (New  Haven)       '..... 

1460 

740 

5495 

Ozark  border  (^^ittenberg)                 

1500 

1660 

5429 

West  Missouri  rolling  prairie  (Garden  City).  .  . 
Southeast  Missouri  lowland  silt  (Hayti)  

3560 
5320 

1445 

4584 

5262 
17785 

Southeast  Missouri  lowland  sandy  soil  (Camp- 
bell)                 

1700 

1711 

3566 

SOIL  FERTILITY 


393 


Plant  Food  in  Soil  Areas  of  Kentucky.3 — Pounds  in  Surface,  0  to  7  Inches, 
Two  Million  Pounds 


Formation 

Total 
nitrogen 

Total 
phosphorus 

Total 
potattsium 

Trenton  

3780 

9416 

26278 

Cincinnatian  

3180 

1924 

31960 

Silurian  and  Devonian 

2480 

1100 

23940 

Waverly  

1960 

650 

19600 

St.  Louis  

2106 

890 

28220 

Chester  .                 .    . 

1700 

702 

26560 

Western  coal  field  .    .          .    . 

1980 

766 

29290 

Eastern  coal  field  (western  part) 

2140 

630 

18180 

Eastern  coal  field  (central  and  eastern  part)..  . 
Quaternary                                           .    . 

2980 
1940 

1260 
980   • 

34213 
30926 

River  alluvium  

3300 

1910 

34430 

Ky  taking  the  figures  of  crop  requirements  given  in  the  tables, 
pages  390  and  398,  it  will  be  easy  to  calculate  the  length  of 
time  necessary  to  completely  exhaust  the  soils  by  growing  maximum 
crops.  This  will  give  a  fair  idea  of  the  deficiency  of  certain  plant 
foods  in  the  soil. 

Nitrogen. — Nitrogen  is  one  of  the  most  limited  of  the  plant 
food  elements  in  soils,  it  occurs  in  organic  matter  in  combination 
with  hydrogen,  oxygen,  carbon,  sulphur,  and  other  elements,  and 
all  non-leguminous  plants  are  indirectly  dependent  upon  this  form, 
legumes  also  use  the  nitrogen  of  the  organic  matter.  Free  nitrogen 
occurs  in  the  soil  air  in  large  quantities,  hut  this  can  be  used  only 
by  legumes.  One  hundred  corn  crops  of  fifty  bushels  each  would 
use  all  the  nitrogen  in  the  surface  soil  of  the  average  brown  silt 
loam,  provided  the  stalks  were  turned  back,  while  if  the  stalks  and 
"rain  were  both  removed  the  nitrogen  would  all  be  used  in  a  little 

~  cj 

more  than  sixty-five  years. 

Through  the  activity  of  soil  organisms  the  soil  nitrogen  of  the 
organic  matter  is  slowly  made  available.  The  process  takes  place 
principally  in  the  plowed  soil  and  the  amount  of  nitrogen  made 
available  each  season  is  approximately  two  per  cent  of  the  total 
nitrogen  in  this  stratum.  If  there  are  four  thousand  pounds  in 
the  plowed  soil,  about  eighty  pounds  will  become  available,  or  an 
amount  sufficient  to  produce  a  fifty-bushel  crop  of  corn. 

Nitrogen  is  the  limiting  element  over  large  areas  of  soil,  and 
its  increase  and  maintenance  becomes  one  of  the  most  important  as 


394 


SOIL  PHYSICS  AND  MANAGEMENT 


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SOIL  FERTILITY 


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SOIL  FERTILITY 


397 


well  as  one  of  the  most  diflicult  problems  for  the  farmer  (Figs.  190 
and  1!)1).  The  methods  that  have  been  recommended  for  main- 
taining the  organic  matter  will  usually  maintain  the  nitrogen,  li 
is  the  most  expensive  plant  food  element,  and  more  of  it  is  required 
hy  crops  than  of  the  other  elements.  When  the  market  price  is 
eighteen  cents  per  pound  the  cost  of  the  nitrogen  for  a  bushel  of 
corn  is  twenty-seven  cents,  for  Avheat  thirty-six  cents,  and  for  oats 


Fro.  190. — Whorit  ({rowing  on  a  soil  very  deficient  in  nitrogen.  Note  the  effect  of  the 
addition  of  nitrogen  (N).  Average  yield  for  nitrogen,  32  grams  per  pot,  without  nitrogen 
3  grains.  (Illinois  Soil  Report.) 


Fio.  191. — Legumes  turned  under  have  the  samp  effect  ns  the  addition  of  nitrogen. 
Yields  for  a  four-year  average  were  u.s  follows:  No  nitrogen,  4  grams  per  pot,  legumes  18 
grams,  and  for  nitrogen  1!()  grams.  (Illinois  Soil  Report.) 

about  eighteen  cents.     This  price  makes  its  purchase  almost,  if  not 
entirely,  prohibitive  for  ordinary  grain  crops. 

Nitrogen  can  be  readily  incorporated  with  the  soil  by  turning 
under  a  crop  of  inoculated  le(/urncs.  These  mav  be  grown  in  con- 
nection with  some  of  the  money  crops,  such  a<  corn,  col  ton.  wheat. 
rye,  oats,  and  others,  and  turned  under  for  soil  enrichment.  The 
cotton  belt  and  the  southern  part  of  the  corn  and  wheat  belt  arc 


398 


SOIL  PHYSICS  AND  MANAGEMENT 


especially  well  adapted  to  this  method.  It  must  be  remembered 
that  nitrogen  is  readily  lost  by  leaching,  especially  after  it  becomes 
available. 

It  would  be  well  to  emphasize  the  necessity  of  turning  the 
legumes  under  instead  of  removing  them.  In  many  places  the 
legumes  are  made  into  hay  and  sold  from  the  farm,  or  fed  without 
returning  the  manure.  Under  these  circumstances  very  little  is 
accomplished  toward  permanent  soil  improvement  by  growing 
legumes. 

Composition  of  Tops  and  Roots.    Crops  Seeded  July  22  (Delaware  Station) 


Crop  and  date  of  harvest 

Air-dry 
matter 

Pounds  per  acre  and 
per  cent  in  roots 

Nitrogen 

Phos- 
'  phorus 

Potas- 
sium 

Cowpeas,  tops  

3718 
301 
9 

65.2 
4.2 
.1 

7.2 
1.0 
.1 

39.2 
1.9 

.1 

Nov.    7,  Roots  0  to    8  inches  

Roots  8  to  12  inches  

Per  cent  in  roots  

8 

6790 
717 
39 

6.0 

130.9 

8.8 
.5 

13.0 

16.5 
1.0 
.0 

8.0 

38.3 
1.4 
.1 

Soybeans,  tops  

Nov.  11,  Roots  0  to    8  inches  

Roots  8  to  12  inches  

Per  cent  in  roots  

10 

3064 
584 
16 

17 

5372 
381 
32 

6.5 

108.0 
12.8 
.4 

5.5 

9.8 
2.0 
.1 

4.0 

65.1 
5.7 
.2 

Vetch,  tops  

Roots  0  to    8  inches  

Roots  8  to  12  inches  

Per  cent  in  roots     

11.0 

128.2 
5.7 
.5 

18.0 

25.9 
.8 
.1 

8.0 

69.7 
3.2 
.3 

Crimson  clover,  tops  

Nov  20  Roots  0  to    8  inches  

Roots  8  to  12  inches     

Per  cent  of  roots  

7 

2267 
1962 
8 

6.0 

54.8 
40.2 
.2 

3.5 

5.7 
3.7 
.0 

5.0 

26.7 
7.9 
.0 

Alfalfa  tops        

*  Roots  0  to    8  inches  

Roots  8  to  12  inches  

Per  cent  in  roots  

47 

2819 
1185 
27 

42.0 

69.8 
32.5 

.7 

39.0 

8.3 
4.3 
.1 

23.0 

38.6 
8.0 
.2 

Red  clover  tops        

Nov  22  Roots  0  to    8  inches  

Roots  8  to  12  inches  

Per  cent  in  roots  

30 

32.0 

35.0 

18.0 

SOIL  FERTILITY  399 

From  the  preceding  table  it  will  be  seen  that  of  the  legumes 
given,  alfalfa  adds  the  largest  amount  of  nitrogen  to  the  soil,  forty- 
seven  per  cent  in  its  roots,  and  red  clover  second  with  thirty-two 
per  cent.  When  the  two  crops  of  red  clover  are  removed  from  the 
land,  the  nitrogen  left  in  the  soil  in  roots  and  stubble  is  on  an 
average  probably  no  more  than  equal  to  that  taken  from  the  soil  by 
the  crop,  so  there  is  no  addition  of  this  element  under  such  a  prac- 
tice. The  table  shows  that  the  roots  of  cowpeas,  soybeans,  and 
crimson  clover  contain  a  very  low  per  cent  of  the  total  nitrogen. 
These  crops  if  harvested  from  the  land  probably  not  only  add  no 
nitrogen  but  actually  remove  some  from  the  soil. 

Fresh  farmyard  manure  contains  about  ten  pounds  of  nitrogen 
per  ton,  and  the  futility  of  trying  to  maintain  this  element  with 
manure  on  the  average  grain  farm  is  readily  seen.  All  manure 
should  be  used  to  the  best  advantage,  but  where  fifty  bushels  of 
corn  per  acre,  and  other  crops  that  remove  equivalent  amounts  of 
nitrogen,  are  grown  it  would  require  about  twenty  tons  of  average 
farmyard  manure  per  acre  every  four  years  to  maintain  it,  even  if 
there  were  no  other  source  of  loss. 

Commercial  Forms  of  Nitrogen.—  The  forms  in  which 
nitrogen  may  be  obtained  commercially  for  use  as  a  fertilizer  are 
as  follows: 

1.  Sodium  nitrate  constitutes  the  principal  form  in  which  the 
element  nitrogen  is  obtained  for  use  in  commercial  fertilizers.    The 
salt  occurs  in  northern  Chili  and  after  being  purified  by  crystalliza- 
tion contains  15  to  1C  per  cent  of  the  element.     Chlorides  and  sul- 
fates  are  present  in  small  quantities.     It  is  very  readily  soluble  and 
should  be  applied  only  when  the  crop  is  growing  to  prevent  loss 
by  leaching,  since  it  is  not  absorbed  to  a  very  great  extent  by  the 
soil.    It  is  used  by  market  gardeners  and  may  be  applied  to  timothy 
meadow  and  small  grains.     Its  continued  use  deflocculates  the  soil, 
producing  a  puddled  condition. 

2.  Ammonium  Sulphate. — Ammonia    is  a   by-product   in   the 
distillation  of  coal  and  the  sulfate  is  produced  by  passing  the  am- 
monia through  sulfuric  acid.     It   contains  about    v()   per  cent  of 
nitrogen.     This  salt  is  readily  absorbed  and  because  of  this  is  not 
so  readily  leached  from  the  soil.     It  should  not  be  applied  in  the 
fall,  because  it  will  l>e  changed  to  nitrates  and  leached  out  and  lost 
Its  continued  use  tends  to  deflocculate  the  soil  somewhat  as  sodium 
nitrate  docs. 


400  SOIL  PHYSICS  AND  MANAGEMENT 

3.  Cyanamid  or  Calcium  Cyanarnid. — This  is  an  artificial 
product  made  by  passing  nitrogen  into  retorts  containing  highly- 
heated  calcium  carbide.  It  is  a  heavy,  black,  granular  powder,  and 
should  be  incorporated  with  the  soil  for  some  days  before  planting 
to  avoid  any  toxic  effect  that  might  be  injurious  to  the  seeds  and 
young  plants.    It  contains  about  16  per  cent  of  nitrogen. 

4.  Organic  Substances. — Certain  materials  that  were  formerly 
waste  products  are  valuable  for  their  nitrogen.     Among  these  are 
cottonseed  meal,  containing  7  or  8  per  cent  of  nitrogen;  linseed 
meal,  with  about  5.5  per  cent;  dried  blood,  containing  from  13  to 
15  per  cent,  and  tankage,  which  has  from  4  to  10  per  cent  of 
nitrogen  and  1  to  8  per  cent  of  phosphorus. 

Phosphorus. — Large  areas  of  land  all  over  the  world  are 
deficient  in  the  element  phosphorus  to  such  an  extent  that  it  be- 
comes the  limiting  factor.  It  is  especially  important  in  the  pro- 
duction of  grain  and  in  the  growth  of  legumes.  Its  addition  helps 
to  make  possible  the  building  up  of  soil  by  larger  growth  of  nitrog- 
enous soil-renovating  crops.  In  addition  to  this  it  improves  the 
quality  and  increases  the  weight  of  the  grain  (Figs.  192  and  193). 

The  needs  of  a  soil  for  phosphorus  may  be  determined  by  apply- 
ing two  hundred  and  fifty  pounds  of  steamed  bone  meal  per  acre  to 
wheat  or  corn  by  sowing  broadcast  before  the  seed  bed  is  prepared 
and  securing  accurate  yields  of  equal  areas  of  the  treated  and  un- 
treated land.  Definite  conclusions,  however,  should  not  be  based 
upon  a  single  year's  results. 

Phosphorus  may  be  purchased  in  several  forms:  (1)  raw  bone 
meal,  (2)  steamed  bone  meal,  (3)  raw  rock  phosphate  or  floats,  (4) 
acid  phosphate,  and  (5)  basic  or  Thomas  slag. 

Bone  meal  is  made  from  the  bones  of  animals  slaughtered  at 
the  packing  houses.  The  bones  are  a  by-product  and  their  high  con- 
tent of  phosphorus  makes  them  valuable.  The  raw  bones  may  be 
ground  up  into  meal,  but  this  contains  three  to  five  per  cent  of 
nitrogen  and  large  amounts  of  fat  and  oil.  The  nitrogen  is  very 
expensive,  while  the  fat  is  of  no  value  to  the  soil.  The  bones  may  be 
steamed  under  high  pressure,  thus  removing  the  fats  and  oils  and 
gelatin.  The  bones  are  then  ground  into  meal  that  is  placed  on  the 
market  as  steamed  bone  meal.  This  contains  less  nitrogen  and  more 
phosphorus  than  the  raw  bone. 

Rock  Phosphate. — Phosphorus  has  been  deposited  in  large 
quantities  as  a  mineral  combined  with  other  elements  forming  the 
tri-calcium  phosphate,  practically  the  same  as  bone  in  composi- 


SOIL  FERTILITY 


401 


(  FARM   MANURE 


Flo.   192. — Wheat,  1011,  I'rbana  field.    Cover  crops  and  farm  manure  plowed  under.    Aver- 
age yield,  34.2  bushels  per  acre.     (Illinois  Soil  Reports.) 


NANUHC 
HOCK   PMOSPHATI 


Flo.  193. — Wheat,  1J>11,  lTrhann  fiolil.  Cover  crops  nnil  fnrm  manure  plowed  under. 
Finrly  ground  rook  phosphate  applied.  Average  yield,  51.8  bushels  per  acre.  (Illinois  -^'U 
Reports.) 

26 


402  SOIL  PHYSICS  AND  MANAGEMENT 

tion.  Large  deposits  are  found  in  South  Carolina,  Florida,  Ten- 
nessee, Utah,  and  other  states.  This  is  mined  and,  when  finely 
ground,  constitutes  the  raw  rock  phosphate  of  commerce.  When 
this  phosphate  is  treated  with  an  equal  weight  of  sulfuric  acid,  the 
resulting  product  is  acid  phosphate.  This  treatment  renders  most 
of  the  phosphorus  available.  It  contains  from  six  to  eight  per  cent 
of  the  element  phosphorus. 

Basic  slag,  a  by-product  formed  in  the  manufacture  of  steel 
from  iron  ores  containing  considerable  phosphorus,  has  been  ex- 
tensively used  in  Europe  as  a  source  of  phosphorus,  but  to  no  large 
extent  in  this  country. 

Forms  Compared. — Of  these  different  sources,  steamed  bone 
meal,  acid  and  raw  rock  phosphate  are  most  commonly  used. 

Without  entering  into  a  lengthy  discussion  of  the  merits  of  each 
of  these,  it  may  be  said  in  general  that  upon  soils  low  in  organic 
matter  acid  phosphate  or  steamed  bone  meal  may  be  used  to  good 
advantage.  If  the  soil  is  well  supplied  with  organic  matter,  finely 
ground  rock  phosphate  will  be  preferable,  since  the  acids  produced 
by  the  decay  of  the  organic  matter  render  the  phosphorus  available. 
Any  form  of  quickly  decaying  organic  matter,  such  as  legumes,  green 
or  barnyard  manure,  will  aid  in  liberating  the  phosphorus.  For  im- 
mediate results  the  rock  phosphate  should  be  applied  before  the 
material  is  turned  under.  It  may  be  added  to  the  soil  for  the  pur- 
pose of  helping  to  obtain  a  catch  of  clover.  For  best  results  with  any 
form  of  phosphate,  limestone  should  be  present  in  the  soil. 

In  the  use  of  phosphorus  on  soils  deficient  in  this  element  the 
one  purpose  should  be  to  increase  the  amount  by  applying  more 
than  is  used  by  the  crops.  A  naturally  fertile  soil  rarely  contains 
less  than  fourteen  hundred  to  sixteen  hundred  pounds  of  the  ele- 
ment per  acre  in  the  plowed  soil. 

Most  upland  soils,  as  shown  by  the  tables  on  pages  392,  393,  and 
394,  actually  contain  from  eight  hundred  to  twelve  hundred  pounds. 
In  the  building  up  of  these  soils  an  excellent  plan  is  to  add  a  ton  of 
finely  ground  rock  phosphate  per  acre  every  four  to  six  years  until 
the  amount  has  reached  that  of  a  normal  fertile  soil,  or  about 
eighteen  hundred  to  two  thousand  pounds  in  the  surface  seven  inches 
of  an  acre.  After  this  is  reached  a  sufficient  amount  should  be 
applied  to  replace  that  removed  by  the  crops. 

The  cost  of  a  pound  of  the  element  phosphorus  is  a  thing  that  is 
frequently  overlooked.  In  bone  meal  and  acid  phosphate  the  cost 
of  a  pound  of  phosphorus  was  about  twelve  and  one-half  cents  per 


SOILS  FERTILITY  403 

pound  in  19 1G,  while  in  the  rock  phosphate  the  phosphorus  cost 
from  two  and  one-half  to  three  cents  per  pound,  depending  upon 
the  distance  from  the  mines,  in  material  containing  fourteen  per 
cent  of  the  element  phosphorus  or  32  per  cent  of  phosphoric  acid. 

If  rock  phosphate  of  the  same  money  value  as  acid  phosphate 
or  hone  meal  were  applied  and  the  conditions  were  at  all  favorable, 
the  results  obtained  would  compare  well  with  those  from  the  other 
forms  and  the  phosphorus  content  of  the  soil  would  be  increased, 
as  so  much  more  of  the  element  would  be  added. 

Potassium. — As  may  be  seen  from  the  tables,  pages  392,  393, 
and  394,  soils  vary  a  great  deal  in  their  content  of  potassium.  Clay 
and  silt  soils  contain  the  most,  while  peats  and  sands  have  least. 
Many  peat  soils  are  so  deficient  in  this  element  that  applications  of 
potassium  are  necessary.  Notwithstanding  the  large  amount  in 
soils,  it  is  sometimes  so  unavailable  that  crops  fail  to  obtain  the 
amount  necessary  for  good  yields.  Potassium  is  usually  locked  up 
in  silicate  minerals  and  the  action  of  acids  of  some  kind  is  necessary 
to  liberate  it.  This  may  be  accomplished  by  the  acids  of  decaying 
organic  matter  which  attack  the  minerals  and  free  the  potassium. 

In  soils  such  as  peat  the  potassium  may  be  supplied  by  applica- 
tions of  potassium  sulfatc  or  chloride,  each  containing  about  eight 
hundred  fifty  pounds  of  the  element  per  ton,  or  kainit.  containing 
two  hundred  pounds  (Fig.  191).  Wood  ashes  contain  five  per  cent 
of  potassium.  Annual  applications  of  one  hundred  to  two  hundred 
pounds  of  the  sulfate  or  chloride  per  acre  are  sufficient  for  most 
crops.  Manure  may  be  used,  but  a  ton  contains  only  eight  pounds, 
and  the  nitrogen  of  manure  has  a  much  greater  value  upon  other 
types  of  soil. 

Other  Elements. — While  several  other  elements  are  required 
for  crops,  the  supply  in  the  soil  is  so  large,  or  the  amount  used  by 
crops  is  so  small,  that  there  is  little  danger  of  a  deficiency.  Sul- 
fur is  required  in  small  amounts,  and  probably  will  need  to  be 
applied  only  in  the  case  of  crops  such  as  turnips,  cabbage,  etc.,  which 
require  large  amounts.  Iron  is  used  only  in  small  amounts  and 
the  soil  contains  an  abundance.  Calcium  and  magnesium  aro  low 
in  some  soils,  especially  acid  ones,  and  may  bo  easily  supplied  in 
limestone,  which  has  been  discussed  in  Chapter  Nil. 

Lime,  Limestone. — All  soils  should  contain  some  carbonate,  but 
more  especially  calcium  carbonate  or  limestone.  Its  presence  is 
very  important  in  the  functioning  of  nitrifying  bacteria  and  the 
production  of  available  nitrogen.  A  base  must  bo  present  to  unite 
with  the  nitrous  and  nitric  acids  formed,  or  the  presence  of  these 


404 


SOIL  PHYSICS  AND  MANAGEMENT 


free  acids  will  inhibit  the  action.  Chemical  combination  takes 
place  and  calcium  nitrites  and  nitrates  are  formed,  the  latter  of 
which  are  available  for  the  use  of  plants. 


FIG.  194. — Corn  on  peaty  swamp  land,  1903.  Lime  and  phosphorus  at  top,  yield  0. 
Lime  and  potassium  at  bottom,  yield  72.5  bushels  per  acre.  (Bulletin  157,  Illinois  Agri- 
cultural Experiment  Station.) 

The  element  calcium  is  used  by  plants  as  food,  as  shown  by  the 
table  on  page  390,  and  there  is  little  doubt  but  that  it  may  be  limit- 
ing the  size  of  the  crops  on  some  soils. 

Soils  frequently  are  acid  or  become  so  after  long  cropping, 
bringing  about  conditions  unfavorable  for  the  growth  of  many 
legumes.  This  acidity  may  be  removed  by  the  use  of  lime,  lime- 
stone, or  some  other  carbonate.  Many  bacteria  cannot  develop  in 
an  acid  soil. 


SOIL  FERTILITY 


405 


Lime  and  limestone  have  a  beneficial  effect  upon  the  physical 
condition  of  the  soil,  since  it  produces  flocculation  or  granulation. 
This  process  is  especially  important  upon  heavy  soils  and  those 
deficient  in  organic  matter,  and  for  this  reason  is  more  beneficial 
when  applied  to  such  soils.  Quicklime  is  more  effective  in  this  way 
than  calcium  carbonate. 


Nitrogen,   Phosphorus  and  Potassium  in  Fertilizing  Materials,   Pounds  Per 
Ton  of  2000  Pounds 


M  atonal 

Nitrogen 

Phosphorus  * 

Potassium  f 

Acid  phosphate                .  . 

114  to  160 

Ammonium  sulfate 

400 

Apatite  

300  to  400 

Ashes,  wood,  leached 

8  to     14 

16  to    50 

Ashes,  w(x)d,  unleached. 

8  to     18 

66  to  132 

Basic  slag  

88  to  160 

Blood,  dried  

260  to  300 

Bone  meal,  raw 

60  to    80 

180  to  220 

Bone  meal,  steamed  

40  to    60 

200  to  220 

Cottonseed  meal  

140  to  160 

18  to    26 

25  to    33 

Kainit  

200  to  220 

Linseed  meal  .    . 

110 

15.6 

226 

Manure,  barnyard,  fresh..  . 
Nitrate  of  soda  

10 
300  to  320 

2 

8 

Phosphate: 
Tennessee  rock  

240  to  300 

Florida  hard  rock 

320 

Potassium  chloride  

820  to  880 

Potassium  nitrate  

260 

730 

Potassium  sulfate  . 

800  to  840 

Tankage,  general  range 

SO  to  200 

20  to  160 

Tobacco  waste  

40  to    80 

4  to  S 

80  to  160 

*  To  find  the  weight  of  phosphoric  arid  (IVH)  per  ton  multiply  the  weight  of  phos- 
phorus by  2..'}. 

t  To  find  the  weight  of  potash  (K»O)  multiply  the  weight  of  potassium  by  1.2. 

Forms  in  Which  Lime  May  Be  Applied. — Lime  may  be  ap- 
plied to  soils  in  several  different  forms.  Quick  or  caustic  lime  may 
be  used,  but  it  is  now  generally  believed  that  it  is  not  the  best  form 
to  apply  because  of  its  tendency  to  encourage  the  decomposition  of 
organic  matter. 

Air-slaked  lime  is  a  form  that  may  be  used,  but  its  extreme  fine- 
ness invites  active  solution  and  loss  by  leaching. 

Marl  is  formed  by  chemical  precipitation  in  small  lakes  in  glacial 
regions,  and  consists  of  a  more  or  less  impure  calcium  carbonate, 
usuallv  somewhat  loose  and  fine.  It  is  only  of  local  sismifieance. 


406  SOIL  PHYSICS  AND  MANAGEMENT 

Limestone  when  ground  so  that  it  will  pass  through  a  screen  of 
ten  meshes  to  the  inch  makes  an  excellent  material  for  applying  to 
the  soil.  The  dust  or  finely  ground  limestone  is  ready  for  imme- 
diate use,  while  the  coarser  part  gives  durability  so  that  applica- 
tions will  not  need  to  he  made  so  often. 

The  Best  Form  to  Apply. — Experiments  have  heen  carried  on 
at  some  experiment  stations  to  test  the  value  of  different  forms.  At 
the  Pennsylvania  Station  two  tons  of  slaked  lime  once  in  four  years 
and  of  ground  limestone  every  two  years  were  used  on  different  plots 
and  the  total  yields  were  greater  for  ground  limestone.  Analyses 
of  samples  from  each  plot  showed  375  pounds  less  of  nitrogen  for 
the  plot  receiving  air-slaked  lime.  Experiments  at  the  Maryland 
Station  gave  larger  yields  for  ground  limestone. 


REFERENCES 

1  Hilgard,  E.  W.,  Soils,  1906,  p.  364. 

'Miller,  M.  F.,   Circular  69,   Missouri   Station,  The  Fertility  of  the  Soil, 

1914,  p.  6. 

•Averitt,  A.  D.,  Bulletin  193,  Soils  of  Kentucky,  Kentucky  Station,  1915, 
p.  141. 

General  References. — Hopkins,  Cyril  G.,  Soil  Fertility  and  Perma- 
nent Agriculture,  1910.  Van  Slyke,  Lucius  L.,  Fertilizers  and  Crops,  1915. 
Hall,  A.  D.,  The  Soil,  1912.  Whitson,  A.  R.,  and  Walster,  H.  L.,  Soils 
and  Soil  Fertility,  1912. 


APPENDIX  II 


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APPENDIX  II  409 

Average  Yield  of  Wheat  Per  Acre  far  Ten  Years  (1905  to  1914}*  Bushels 


United 

States 

Russia 
(European) 

Germany 

A  11.  -i  ri:i 

Hungary 
proper 

France 

United 
Kingdom 

14.8 

9.9 

30.7 

20.0 

18.1            20.1 

33.4 

*  Yearbook  U.  S.  D.  A..  1915. 


APPENDIX  III 

THE  following  maps  are  taken  from  the  Yearbook  of  the  United 
States  Department  of  Agriculture  for  1915 : 


2  S  S  s  !  5  i 
I  I  I  I  I  I 
I S  9  f  1 1 1 


410 


APPENDIX  III 


411 


412 


APPENDIX  III 


APPENDIX  III 


413 


414 


APPENDIX  III 


APPENDIX  III 


415 


416 


APPENDIX  III 


APPENDIX  III 


417 


INDEX 


Ablation  swamp,  30 
Absolute  specific  gravity,  175 
Absorbents,     factor     in     conserving 

manure,  165 

Absorption   and    radiation   of    heat, 

effect  of,  on  soil  temperature,  302 

Acclimated    seed,    desirable    on    dry 

land,  255 

Accumulations  in  pastures,  aid  in 
maintaining  organic-matter  con- 
tent, 160 

Acid,  chromic,  method  of  determina- 
tion of  organic  matter,  154 
phosphate,  402 

Acids,  decomposition  of  rocks  by,  11) 
carbonic,     hydrochloric,     nitric, 

sulfuric,  20 
Acre-inches,  1!)2 

Adaptation  of  region   to  dry   farm- 
ing, factors  in,  238 
evaporation,   241 
rainfall,  238 
soils,  241 
Adol>e,  65 

Adsorption  by  colloids,  132 
Aeration   and   soil   air,   chapter  on, 

309 

affecting  bacteria,  320 
aided  by  drainage,  223 
or  soil   ventilation,   311 

accomplished   by   atmospheric 
pressure,  changes  in,  311 
diffusion,  311 
removal  of  water,  311 
temperature  changes,  312 
tillage,  313 
wind  movement.  313 
Aftonian   Inter-glacial  Stage,  46 
Agassi/,   F,ake,   38 

extent  of,  46 
Agencies  of  weathering,  chemical,  11) 

physical.   12 

Agricultural  provinces,  383 
Agriculture,    dry-land,    chapter    on, 

238 

permanent,  389 
Air  in  soils,  amount  of.  309 

convection  currents  of,  source  of 
loss  of  heat,  296 


Air  in  soils,  composition  of.  310 

use  of,  309 
Alfalfa,  completely  killed  by  heaving, 

226 

crop  for  dry  land.  253 
Alkali,  area,   absence  of   vegetation 

on,    286 

black,  neutralization  of,  281 
effect  of   irrigation   on   rise  of, 

281 
on    foliage    of    apricot    trees, 

283 

on  plants,  282 
kinds  of,  280 
land,  growth  of  barley  on.  partly 

and  fully  reclaimed,  288 
reclaimed,  wheat  on,  289 
lands,    and    their    reclamation, 

chapter  on,  278 
utilization     and     reclamation 
of,   by   removal   of  alkali 
salts,'  285 
growing       alkali  -  resistant 

crops,  2S5 
neutralizing     black     alkali, 

286 
plowing   deep   and    turning 

alkali  under,  286 
retarding  evaporation,  285 
limit     for     germination     and 

growth,  284 
origin  of,  278 

resistant  crops,  growing  of,  285 
rise  of,  prevented  bv  cultivation, 

286 

drainage,  226 

salts,  removal  of.  by  cropping, 
draining,  flooding,  leaching, 
scraping,  287 

soils  of  humid  regions,  reclama- 
tion of,  290 

spot,  beginning  of,   279 
turning   under  of,   286 
Alluvial   soils,   38 
Alluviation  by  glacial  stream.  62 
Altitude,  affecting  organic  content  of 

soils,  145 

Ammonia,  effect  on  flocculation,  137 
Ammon  iff  cation,  318 

419 


420 


INDEX 


Ammonium  sulfate,  399 
Amphibole,  3 

Analyses,  chemical,  of  adobe,  65 
Analysis,    mechanical    or    physical, 

123 

physical,  systems  of,  124 
Andesite,   7 

Animals,  decomposition  by,  25 
Apatite,  calcium  phosphate,  5 
Appalachian  Mountain  and  Plateau 

Province,  81 

Apparent  specific  gravity,  175 
Aqueous  rocks,  7 

Area,   and   projects,    irrigation,   258 
internal,  of  soil  types  calculated 
from     physical     composition, 
182 

of  soil  surveyed  in  the  United 
States  by  Bureau  of  Soils  to 
1915,  78 

of  spheres,  columnar  arrange- 
ment, 181 

or  internal  surface,  181 
Arid  soils,  74 

nitrogen  in  humus  of,  147 
subsoils,  and  humid,  70 
Arrangement  of  particles,   179 

columnar,  area  of  spheres,   181 

or  vertical,  180 
oblique,  180 

Artificial  mulch,  defined,  233 
Aspirator,  King's,  128 
Atkinson,  A.,  and  Nelson,  J.  B.,  stor- 
ing rainfall,  Montana,  248 
Atlantic    and    Gulf    Coastal    Plains 

Province,  91 

Atmosphere,  carbon  dioxide  in,  20 
Atmospheric    pressure,    changes    in, 

factor  in  aeration,  311 
effect  on  percolation,  219 
Auger,  soil,  119 
Available  moisture,  214 

increased  by  drainage,  223 
Averitt,   A.   D.,   plant   food   in    soil 
areas  of  Kentucky,  393 

Babb,    table,    sediment    carried    by 

streams,  35 
Bacteria,  conditions  for  development, 

319-321 
aeration,  320 
food,  319 
light,  321 
moisture,  319 


Bacteria,     conditions     for     develop- 
ment, physical  composition 
of   soil,    321 
reaction,  320 
temperature,  320 
distribution  of,  318 
number  of,  effect  of  lime  upon, 

321 

per  gram  of  air-dry  soil,  319 
Bacterial  action,  effect  of  potassium 

carbonate  upon,  321 
Barley,  yield  of,  continuous  cropped 

vs.  after  fallow,  249 
Barnyard  manures,  161 
Barometric  pressure,  changes  in, 

factor  in  aeration,  311 
Bartlett,  W.  H.,  expansion  of  rocks 

on  heating,  13 
Basalt,  7 
Basic  slag,  402 
Bates,  with  Lynde,  osmosis  in  soils, 

212 

Beach  or  Marram  gras-s,  transplant- 
ing, 56 
Beavers,  J.  C.,  manure  excreted  by 

farm  animals,  162 
value   of   increase   for   manure, 
heavy  and  light  applications, 
168 
Bennett,  H.  H.,  Bureau  of  Soils,  soil 

survey,  78-111 
Biological  effects  of  organic  matter, 

150 

Biotite,  black  mica,  4 
Black  alkali,  neutralization  of,  286 
Black  locusts,  hold  sand,  59 
prevent  washing,  368 
"  Blowout,"  in  sand  dune,  59 
Bog,  climbing,  28 

quaking,  28 

Bogs,  see  hummocks,  30 
Boiling  and  freezing  points,  colloids, 

effect  on,  131 
Bone  meal,  400 
Boulder,  granite,  51 

limestone,     showing    glacial 

scratches,  42 

Boulders,  from  moraine,  51 
Bouyoucos,  G.  J.,  effect  of  color  on 

radiation,  295 
on    temperature    of    sands, 

302 

specific  heat  of  soil  constituents, 
299 


INDEX 


421 


Bouyoucos,  G.  J.,  time  for  heat   to 

penetrate  soil.  30(» 
Briggs,  L.  J.,  ratio  between  viscosity 

and  How  of  water,  219 
thickness    of    hygroscopic    film, 

194 

Briggs,  Martin,  and  Pearce,  Bureau 
of  Soils,  sizes  of  particles, 
124 

chromic  acid  method  of  deter- 
mining organic  matter,  154 
Briggs  and  Me  La  no.  moisture  equiv- 
alent centrifuge,  202 
Briggs   and    Sliant/.,    water    require- 
ment     of      plants,      Akron, 
Colorado,   242 
wilting  coefficient,  212 

determination  of,   107 
Brown,    E.    K.,    with    Schreiner,    ()., 

progress  of  humitication,   14(> 
Brown,   1'.   K.,  bacteria  per  gram  <>f 

air-dry  soil,  .SI!) 
Brownian   movement,    130 
Buckingham,  little  loss  of  water  by 

interstitial    evaporation,    232 
Bureau  of  Soils 

centrifugal    method   of   physical 

analysis,    127 
classification    of    soils,    chapter 

on,  7H 

grades  of  soil  particles.  124 
provinces,  soil 

Appalachian  Mountain  and 

Plateau,  SI 
Atlantic,  and   (!ulf    Coastal 

Plains,  ill 

(Macial  and   l.ocssial,  84 
(ilacial  Ijikc  and  River  Ter- 
race, 8!» 
Limestone  Valleys  and  I'p- 

lands,  S3 

Piedmont  Plateau,  7!> 
Kiver   Flood   Plains,  97 
regions,  soil 

Arid    Southwest.    10<i 
(.•rent    Basin,    10I» 
(Jrcat   Plains.    100 
Northwest      Intel-mountain, 

105 

Pacific  Coast,  107 
Rocky    Mountains,    101 
series,  soil 

Aeadia.  92 
Alamancc.    7!> 
Altamont,    107 


Bureau  of  Soils, 
series,  soil 

Amarillo,  103 
Arkansas,  104 
Bangor,  84 
Bates,   100 
Benton,    101 
Berks,  81 
Bibb,  97 
Billings,   105 
Bingham,  100 
Blanco,   97 
Boise,    105 
Boone,    101 
Brennan,  92 
Brooks,  83 
Caddo,    92 
Cahaba.  97 
Caldwell,  106 
C'ameron,  97 
Canyon,  102 
CarilM>u,  84 
Carrington.  84 
Ca/enovia,   85 
Cecil,  79 
Chehalis,  110 
Chenango,   89 
Chester.    80 
Cheyenne,    104 
Clark,   101 
Clarksville,   83 
Clyde.  89 
Colbert,  83 
Colby,  102 
Coloma,    85 
Colorado,  103 
Conasauga,  81 
Conestoga.  83 
Conga rec.  !»7 
Corning,   107 
Cossaymna.  85 
Coxvi'lle.   92 
Crawford.  101 
Crowley.   93 

Dawes.  1 03 

Decatur.  S3 
DeKalb.  SJ 
Dunkirk.  90 
Durham.    SO 
Dutches*.  85 
Duval,  93 
Durant.   93 
Kdna.  93 
Klktou.  93 


422 


INDEX 


Bureau  of  Soils, 
series,  soil 

Englewood,  101 
Ephrata,  105 
Eppihg,  101 
Everett,  108 
Fargo,  90 
Fayetteville,  82 
Flushing,  85 
Fox,  90 
Fresno,  108 
Frio,   98 
Ganett,  103 
Genesee,  98 
Gila,   107 
Glendale,  107 
Gloucester,  85 
Goliad,  93 
Greensburg,  103 
Greenville,  93 
Hagerstown,  83 
Halston,  98 
Hanceville,  82 
Hanford,  108 
Hesson,  108 
Holyoke,  86 
Houston,  93 
Huntington,  98 
Imperial,  107 
Indio,    107 
Iredell,  80 
Jordan,   106 
Kalmia,  98 
Kewaunee,  86 
Knox,  86 
Lackawanna,  86 
Lake  Charles,  94 
Lansdale,  80 
Laramie,  105 
Laredo,  98 
Laurel,  104 
Leonardtown,  94 
Lexington,  86 
Lincoln,  104 
Lintonia,  98 
Louisa,  80 
Lufkin,  94 
Lynden,  109 
Manchester,  90 
Manor,  80 
Maracopa,  109 
Marion,  86 
Marshall,  86 
Maverick,  94 
Meigs,  82 
Melbourne,  108 


Bureau  of  Soils, 
series,  soil 

Memphis,  87 
Merrimac,  90 
Mesa,  105 
Miami,  87 
Miller,  98 
Mohawk,  87 
Monroe,  94 
Morton,  101 
Myatt,  99 
Nueces,  94 
Ocklocknee,  99 
Oktibbeha,  95 
Olympic,  109 
O'Neill,  102 
Ontario,  87 
Orangeburg,  95 
Orono,   90 
Osage,  99 
Oswego,  101 
Oxnard,  109 
Penn, 80      . 
Pierre,  101 
Placentia,    109 
Plainfield,  90 
Plymouth,  87 
Podunk, 99 
Porters,  82 
Portsmouth,  95 
Pratt,  103 
Puget,  111 
Putnam,   87 
Quincy,  105 
Redding,  110 
Richfield,   103 
Richland,  87 
Rosebud,  103 
Ruston,  95 
Sacramento,  111 
Salem,  111 
San  Antonio,  95 
San  Joaquin,  109 
San  Luis,  104 
Sarpy,  99 
Sassafras,  95 
Scranton, 96 
Sharkey,  99 
Shelby,  88 
Sidney,  101 
Sioux',  91 
Stockton, 110 
Summit,  102 
Superior,  91 
Susquehanna,  96 
Talladega,  82 


INDEX 


423 


Bureau  of  Soils, 
aeries,  soil 

Tifton,  90 
Trinity,  99 
Tripp,  104 
Trumbull,  88 
Union,  88 
Upshur,  82 
Uvaldc, !»!) 
Valentine,  102 
Vergennes,  91 
Vernon,    102 
Victoria,  90 
Volusia,  8S 
Wabash, !)!) 
Wade,  104 
Walla  Walla,  105 
Waukesha,  91 
Waverly,   100 
Webb,  90 

Westmoreland,  82 
Whatcom,  110 
Wheeling,  100 
Williams,  8.8 
Willows,  110 
Wilson,  06 
Winchester,    105 
Wooster,  88 
Yakima,  10(5 
Yaxoo,  100 
Volo,  110 
York,  81 
Yuma,  107 
Zapata,  103 

Calcareous  rocks,  clialk,  7iiarl,  8 
('alette,  calcium   carbonate,  5 
Calcium  carl>onatc,  caleite,  5 

carried  by  Thames  River,  23 
concretions,    02 
cyan  a  in  id,  400 

magnesium    carbonate,    dolo- 
mite, 5 

sul fate,  gypsum,  5 
Call,    L.    K.,   methods   of    preparing 

land  for  wheat,  347 
Campbell,    II.    W.,    pioneer    in    dry 

farming,  247 

subsurface  packer,  247,  337 
Canals,  loss  of  water  from,  2(50 
Capillarity,  amount  of  water  moved 

by,  210 
Capillary    lift    of    soil    constituents, 

212 
pull  of  soils,  211 


Capillary  capacity  or  moisture-hold- 
ing capacity  of  soils,  209 
rise    of    water    in    glass    tubes, 

height  of,  199 

rapidity  and  height  in  dif- 
ferent soils,  207 
water  as  films  or  waists  about 

particles,   200 
in     covered     and     uncovered 

soil,  204 

of  soils,  chapter  on,  199 
movement,     affected     by     or- 
ganic matter,  20(5-208 
substances  in  solution,  205 
temperature,  204 
texture.  20(5 
thickness  of  film,  203 
viscosity,  204 
use  of,  212 
Carbonated  water,  almost  universal 

solvent,   20 
Carbon  dioxide 

aid  in  solution,  22 
brought   to   earth   in   precipi- 
tation, 20 

decomposition  by,  20 
in  rain  and  snow  water,  20 

soil  air  and  atmosphere,  20 
Catch  and  cover  crops,   1(51 

aid    in    preventing   erosion, 

3(52 

Cafes,  J.  S.,  and  Cox,  If.  It.,  results 

of  corn  cultivation,  28  states,  353 

Caves,  due  to  action  of  carbonated 

water,  22 

('•enters     of     accumulation,     Cordil- 
lera n,      Keewatin,      Labra- 
dorean,  45 
map  of,  47 

Centrifugal   clutrialor,  Yoder's,   128 
method     of     physical     analysis. 

Hureau  of  Soils,  127 
Chains,  for  puddling  mud  of  canals 

to  prevent  seepage.  207 
Chalk,  8 
Characteristics    of    water,    physical. 

180 

Chemical  agencies  of  weathering.  1!) 
changes  in  soil,  source  of  heat, 

294 

precipitates,  8 
Chernozem    soils,   roots  and   humus 

in.    144 
Chester.    F.    K..   effect   of   lime  upon 

number  of  bacteria,  321 
Chicago,  Lake,  38 


424 


INDEX 


Chromic      acid,      and      combustion 
methods,     comparison,    or- 
ganic matter,  155 
method    of    determination    of 

organic  matter,  154 
Churn  elutriator,  physical  analysis, 

Hilgard,  126 

Cippoletti   or   trapezoidal   weir,   209 
Classes,   types   and   phases,   in   Illi- 
nois, 114 
Clay,  defined,  134 
dunes,  53 

effect  of,  on  shrinkage,  133-135 
loams,  115 
tight,  68 
Clays,  114 

and    clay    loams,    properties    of 
coagulation    or    floccu- 
lation,  137 
plasticity,  135 
puddling,  136 
shrinkage,  135 
tenacity,  134 
Clark,  F.  W.,  composition  of  known 

earth,  2 
Classification  of  soils,  by  Bureau  of 

Soils,   chapter  on,   78 
based  on  color,  77 
geology,  72 
lithology,       the       parent 

rock,  73 
moisture,  73 
temperature,  73 
texture,  77 
vegetation,  75 
need  of,  72 
Cleavage,   vertical,  characteristic  of 

deep  loess,  o3,  64 
Coagulation  or  flocculation  of  clays, 

137 

Coal,  formation  of,  from  organic  mat- 
ter, 146 
Coffey,  G.  N.,  dark  color  indicating 

outcrop  of   limestone,   177 
lime  and  magnesia  in  soils,  75 
mineral  content  of  soils,  74 
reports  clay  dunes  in  Texas,  53 
soluble  salts  in  soils,  74 
Colloids,  affecting  hygroscopic  moist- 
ure, 195 

dialysis  and  diffusion  of,  131 
examples  of,   129 
in  soils,  132 

organic  and   mineral,   132 
properties  of,  130 
adsorption,  132 


Colloids,  properties  of,  boiling  point, 

effect  on,  131 

Urownian   movement,    130 
dialysis,    130 
diffusion,   130 
electrical   behavior,   131 
freezing  point,  effect  on,   131 
shrinkage,   132 
size  of  particles,  130 
Colluvial  soils,  30 
Color  of  soils,  176 

changed  by  erosion,  361 
effect  of  deoxidation  on,  21 
on  temperature,  303 

of  sands,  302 

factor   in   classification,   77 
Colorado  mud-flow,  34 
river,  work  of,  17 

Grand  Canon,  17 
Columbia  glacier,  over-riding  forest, 

Alaska,  14 
front  of,  15 
Columnar  arrangement  of  particles, 

180 

Combustion  and  chromic  acid 
methods,  comparison,  organic 
matter,  155 

in  oxygen  determination  of  or- 
ganic matter,   154 
Compacters,  bar  roller,  337 
corrugated   roller,   336 
cultipacker,   336 
drum  roller,  335 
plankers,  337 
subsurface  packer,  337 
Compacting  the  soil,  a  part  of  till- 
age, 326 
increases    moisture    capacity, 

230 

Composition  of  feldspars,  3 
fresh   manure,    163 
known  earth,   2 
river  sediments,  262 
Concrete  dams  for  filling  gullies,  373 
Concretions,  calcium  carbonate,  63 

iron, 64 
Conductivity    of    soil,    effect    of,   on 

temperature,  306 
material,  306 

Constituents  of  soils,  mineral,  chap- 
ter on,  123 

organic,  chapter  on,  142 
Contour  plowing,  deep,  aid  in  check- 
ing erosion,  364 

seeding,  aid  in  checking  erosion, 
365 


INDEX 


425 


Control  of  moisture,  chapter  on,  222 
Cordilleran  center  of  accumulation, 

45 

Corn,  acreage,   1909,  412 
belt  rotations,  382 
comparison,  cultivated,  scraped, 

weeds  allowed  to  grow,  351 
cultivation,  353 

effect  on  yield  of  root  pruning 
and  deep  and  shallow  cultiva- 
tion, 355 
grown  on  dry  land,  252 

on  swamp  land,  effect  of  po- 
tassium- on,  404 
method   of    preparing   seed   bed 

for,  348 
planter,  338 
production,   1909,  413 
results  of  cultivation,  352 
yields  of,  different   methods   <>f 

tillage,  354 

Cotton  belt,  rotation  for,  384 
Cottrell,  II.  M.,  pounds  seed  per  acre 

for  different  crops,  255 
Cover  and  catch  crops,  161 
Cox,   II.   II.,   with    Cates,   J.   S.,   re- 
sults corn   cultivation,  28   states, 
353 
Cracks,  in  black  clay  loam,  136 

shrinkage,  effect  of,  on  percola- 
tion, 219 
Cropping,    alternate    rs.    continuous, 

yields,  250 
continuous     vs.     after     fallow, 

wheat  yields,  Montana,  248 
IOBS  of  organic  matter,  due  to, 

151 

systems  of,  248 

Crop  requirements,  plant   food,  390 
Crops,   alkali-resistant,   growing   of, 

on  alkali   land,  285 
catch  and  cover.   161 
deep  rooting,  effect  of,  345 

on  moisture  capacity,  171 
for  dry   farming,   see   dry-farm- 
ing crops 
for  irrigated  land,  see  irrigated 

land,  crops  for 

non-tilled,    factor    in    maintain- 
ing organic  matter,   171 
plant  food  in,  390 


Crops,    protection    from   erosion    by 

catch  and  cover,  362 
meadows  and  pastures,  361 
rotation  of,  aid  in  maintaining 

organic  matter,    171 
ten-year    average    yield    of,    by 
states  in  United  States,  407, 
408 
Crystalloids,   dialysis   and   diffusion 

of,    131 

Cultivation  after  irrigation,   273 
and  summer  tillage  in  dry  farm- 
ing, 246 
level,  355 
object   of,   350 
of   corn    on   gray   silt   loam   on 

tight  clay,  yields,  353 
of  corn,  Illinois  yields.  352 
results  of  deep  and  shallow,  with 
and     without    root    pruning, 
corn,  355 
ridged,  356 
Cultivators,  337 
blade,  339 
disk,  339 
shovel,   338 
weeder,  340 
Cumulose  soils,  27 
Currents    of   air,   convection,   source 

of  loss  of  soil   heat,   2!Hi 
Cyanamid,  calcium,  400 

Dams,    for    filling    gullies,    concrete, 

273 

earth,  271,  272 

Deacon,   (J.  I1'.,   relation   between   ve- 
locity  and    amount   of   ma- 
terial carried  by  streams,  .'!:{ 
Debris  cliff,  30 
Decomposition,  effect  of,   on   loss  of 

constituents  of  rock,  22 
of  organic  matter  by  drainage, 

225 

of  rocks,  1 1 
by  acids,  19 
by  animals,  25 
by    plants.    25 
tli rough  solution,  22 
Deep-rooting  crops,  etl'eet  of,  345 

on    water    capacity    of    soil. 

•_>::i 

Deherain,  effect  of  aeration  on  nitri- 
fying  bacteria.   •'!-<> 
loss  of  nitrates  by  leaching.  '\'2'2 
Denitrification,  nitrates  lost  by,  3'2.'l 


426 


INDEX 


Density,    with    surface    tension    of 

solutions,  206 
Deoxidation,  21 
Deposits,  eolial,  53 

glacial   or  ice-laid,  chapter  on, 

41 

Determination  of  humus,  156 
Diabase,  7 

Dialysis  and  diffusion,  colloids,  crys- 
talloids, 131 
of  colloids,  130 
Diffusion,  factor  in  aeration,  311 

temperature  for,  298 
Digestibility  of  feeds,  162 
Diorite,  7 

Disintegration  by  plants,  19 
by  waves,   18 
by  wind,  18 
of  rocks,  11,  32 
Distribution  of  alkali,  vertical  and 

horizontal,  281 
of  irrigation  water,  268 
Ditches,  open  drains,  226 
Dobeneck,   hygroscopic   moisture    in 
relation    to    relative    humidity, 
196 

Dolomite,    calcium    magnesium   car- 
bonate, 5 
Dorsey,  C.  W.,  reclamation  of  alkali 

land  by  underdrainage,  289 
alkali  at  Maryland  station,  290 
Drain  gages,  220 
Drainage,  chapter  on,  222 

benefits   of,   aeration   improved, 

223 

alkali,  rise  of,  prevented,  226 
decomposition    and    nitrifica- 
tion increased,  225 
erosion  decreased,  226 
granulation  improved,  222 
heaving  reduced,  225 
moisture,        available,        in- 
creased, 222 
stability  increased,  222 
temperature  raised,  225 
effect    of,    on    germination    and 

growth,  223 

on  soil  temperature,  301 
from  8  feet  of  saturated  sand, 

221 
types  of,  open  or  ditches,  226 

tile,  228 

Drains,   see  Drainage 
Drills,  seeders,  337 
Drumlins,  44 

formation  of,  45 


Dry-farming,  crops  for  alfalfa,  253 
barley,  251 
corn,  251 
emmer,  252 
kafir,  252 
milo  maize,  252 
oats,  251 
potatoes,  253 
rye,  251 
sorghum,  252 
spelt,  252 
wheat,  250 
deep,  medium-grained  soil  well 

adapted  to,  243 
Dry-land     agriculture,    chapter    on, 

238 
Dumont,  effect  alkaline  carbonate  on 

nitrate  production,  321 
Dunes,  clay,  sand,  silt,  53 
permanent  or  fixed,  55 
wandering,  migatory,  54 
Dupr6,   with   Lynde,  capillary   pull, 

211 

osmosis  in  soils,  212 
Dust  and  loess,  physical  analysis  of, 

64 

storm,  54 
volcanic,  65 
Dynamiting  of  soils,  345 

Earth,  composition  of,  2 

dam  for  filling  gullies,  371,  372 
Earth's  crust,  elements  of,  1 
Earthworms,  aid  in  soil  formation, 

315 

effect  of,  on  soil,  25 
Eel-grass,  37 
Elements  of  earth's  crust,  1 

plant  food,  390 

Electrical  behavior  of  colloids,  133 
Elutriator,  method  of  physical  analy- 
sis, Schone,  124 
churn,  Hilgard's  126 
centrifugal,  Yoder's,  128 
Eolial   deposits,  or   wind-laid   soils, 

53 

adobe,  in  part,  64,  65 
loess,   60-64 
sand,  53-64 
volcanic  dust,  65 

Eroded  hill  lands,  yield  from,  360 
soil  once  forested,  China,  359 
Erosion,  chapter  on,  357 
cause  of, 

rainfall,  character  of,  359 
texture  and  structure  of  soil, 
358 


INDEX 


427 


Erosion,  cause  of,  topography,  effect 

of,  358 

vegetative  covering,  359 
checked  by  brush,  372 
decreased  by  drainage,  226 
by  organic  matter,   150 
headwater,  372 
in  pasture,  370 
kinds  of,  sheet,  361 

gullying,  369 
of  streams,   16 
old-field  in  Mississippi,  370 
organic  matter  lost  by,  151 
results  of,  color  of  soil  changed, 

361 
organic  matter  and  nitrogen 

removed,  360 
physical     character     of     soil 

changed,  360 

sheet,  methods  of  prevention  and 
reclamation,  contour 
seeding,  365 
crops,     protection     by, 

361 
deep   contour    plowing, 

364 
limestone,     application 

of,  361 

organic      matter,      in- 
creasing. 363 
reforesting,  369 
residues,    363 
terracing,  3(55 

tiling,  369 
Eruptive  rocks,  6 
Esker,  Adeline,  44 

material  composing  it,  45 
formation  of,  45 

Evaporation,  effect  of,  on  soil  tem- 
perature,  300 

factor   in  adaptability   of  a   re- 
gion to  dry  farming,  241 
from   a    free-water   surface   and 

rainfall,  241 

large    loss    from,    in    dry    farm- 
ing, 243 

loss    by,    effect    on    transpira- 
tion, 191 

of  water,  cools  soil,  296 
prevented  by  mulches,  232 
rainfall  and,   Rothamsted,  211 
rainfall   and   percolation.   Hoth- 
amsted, 220 
retarding  of,  factor  in  cropping 

alkali    land.   285 
Everglades,   Florida,  29 
Exfoliated  granite  in  California,  13 


Expansion,  enormous,  due  to  hydra- 

tion,  21 

due  to  oxidation,  21 
of  rocks,   13 

Expressing  moisture  content,  ways 
of,  191 

Fall  plowing,  342 

Fallow,  continuous  vs.  after,  wheat 

yields,  Montana,  248 
Fallowing,    loss    of    organic    matter 

by,    153 
Farm  land,  value  per  acre,  410 

property,  value  per  acre,  411 
Feeds,    digestibility    of,    162 
Feldspars,  3 

composition  of,  3 
Fermentation   in   manure,   factor   m 

loss  of  organic  matter,  164 
Fertility    in    Illinois    soils,    394-396 
Films    and    waists    of    water    about 

particles,  200 

thickness  of,  in  soil  column,  201 
Fine  sandy  loams,  116 
Fippin,  E.  O.,  with  Lyon,  T.  L.,  sur- 
face  tension   and   density   of   cer- 
tain   solutions,    206 
Fires,    organic   matter   lost    by,    152 
Fischer,  carlxm  dioxide  in  rain  and 

snow  water,   20 

Flocculation,  effect  of  ammonia, 
lime,  gypsum,  sodium  carlx>n- 
ate  on,  137 

or  coagulation  of  clays,  137 
Flooding  orchards,  basin  system,  '270 
Florida  everglades,   29 
Flow  of  water,  comparison  l>etween 

computed  and  observed,  129 
Food  for  bacteria,  319 
Forl>es,  R.  H.,  vnlue  of  material  car- 
ried by  Salt  River.  262 
Forest,  being  buried  by  sand  dune,  55 

resurrected.  55 
Fragmental   deposits.   8 
Freezing    and     boiling    points,    col- 
loids, effect  on,  131 
and    thawing.    14 

effect  on  water  logged  soil.  22.S 
Furrow  irrigation  of  potntoes.  271 

Geological  classification  of  soils.  72 
<!corgeson,    influence    of    manure   on 

soil  temperature,  294 
Germination   and   growth,   effect  of 

drainage    on.    223 
limit   of  alkali    for.   284 
temperature  for.  296 


428 


INDEX 


Gilbert   with   Lawes,    transpiration, 

188 

Glacial  and  loessial  province,  84 
drift,  gravelly  phase,  41 
grooves,  striae,  43 
lake  and  river  terrace  province, 

89 
lakes,  50,  51 

extent  of,  46 
or  ice-laid  deposits,  chapter  on, 

41 

period,  45 

scratches  on  boulder,  42 
stream,  alluviation  by,  62 
Glaciation,     extent     of,     in     North 

America,   map   of,   46 
in   Europe,   map   of,   48 
Glaciations,  Illinoisan,  47 
lowan,  48 

Jerseyan  or  Nebraskan,  46 
Kansan,  46 
Wisconsin,  Early,  50 

Late,  50 

Glacier,    Chenega,    41 
Columbia,  front,  15 

over-riding  forest,  Alaska,  14 
defined,    16 

factor  in  weathering,  15 
incidental  features,  50 
pressure  of  ice,   16 
Grand   Canon,   Colorado   River,    17 
Granite,  7 

exfoliated,  California,  13 
wind-carved,    18 
Oranulation,   effect   of  drainage  on, 

222 

of  organic  matter  on,  148 
of,  on  percolation,  218 
Grass,  beach  or  Marram,  transplant- 
ing, 56 

bunch,  holds  sand,  60 
Gravel  and  gravelly  loams,  139 
Gravelly  loams,  116 
Gravels,    116 

Gravitational  water,  chapter  on,  217 
Gravity-laid  soils,  30 
Great  Basin   region,   106 

Plains   region,   100 
Green  manures,   160 
Growth   and   germination,   effect   of 

drainage  on,  223 
color  of  soils  on,  303 
of  plants,  limit  of  alkali  for, 

284 

temperature  for,  297 
Guide-row  terrace,   365 
Gulf  Coastal  Plains,  and  Atlantic,  91 


Gullying,  methods  of  prevention  and 
filling,  dams,  371 

soil,  374 

straw  and  brush,  370 

vegetation,  374 
Gypsum,  5 

Haberlandt,  time  required  for  ger- 
mination at  different  tempera- 
tures, 297 

Hall,   A.   U.,    rainfall   and   evapora- 
tion, Rothamsted,  211 
table,  rainfall,  percolation,  evap- 
oration,   Rothamsted,    220 
temperature  of  soil  for  growth, 

298 
yield  of  wheat  with  percolation 

large  and  small,   153 
Hardness  of  minerals,  2 
Hardpan,   69 

effect  of,  in  alkali  lands,  290 
Harrows,  acme  or  blade,  333 
disk,    334 
spike- tooth,   331 
spring-tooth,  332 
Hay  and  pasture  province,  rotation 

for,  386 

Heat,   absorption   and   radiation   of, 
effect  on  soil  temperature,  302 
and   cold,   factor   in   disintegra- 
tion,  12 
conduction  downward  into  soil, 

source  of  loss,  296 
soil,  sources  of,  293 
specific,  affecting  soil  tempera- 
ture, 298 

effect  of  moisture  on,  300 
of  common  substances,  299 
of  soil  constituents,  299 
of  soils,   300 

to  penetrate  soil,  time  for,  306 
Heaving,   due   to   lack   of   drainage, 

225 

of  alfalfa,  226 
"Heavy"  soil,  denned,  134 
Hellriegel,     water     transpired      per 

pound  of   dry  matter,    188 
Hematite,  5 
Hilgard,  E.  W.,  changes  in  organic 

matter,  146 
churn  elutriator,  126 
composition    of    salts    in    alkali 

spot,  282 

of  typical  alkali  salts,  280 

effect  of  various  substances  on 

hygroscopic   capacity,    195 


INDEX 


429 


ililgard,  E.  W.,  fertility  in  Russian 

soils,  392 

force  exerted  by  roots  in  pene- 
trating soil,    1!) 
grades  of  soil  particles,  system 

of,  124 
highest   amount  of   alkali   with 

plants  unaffected,  284 
hygroscopic    capacity    of    soils, 

194 

nitrogen  content  of  humus,   1!)4 
on  use  of  hygroscopic  moisture, 

198 
roots    and     humus    in     Russian 

soils,    144 
vertical    distribution    of    alkali, 

281 
Hopkins,  C.  (1.,  grades  of  particles, 

system  of,   124 
production   of   sweet   clover   per 

'acre,  173 

Humid   and    arid    subsoils,   70 
regions,  alkali  of,  290 
soils,    75 

nitrogen  in  humus  of,  147' 
Humidity,      affecting      hygroscopic 

moisture,   190 

Humilication,  progress  of,  140 
Hummocks,  called   lx>gs,  30 
Humus,  defined,    142 

determination    of,    15(5 
in  Chernozem  soils,  144 
nitrogen   content  of,    147 
llydration,  21 
Hydrochloric    acid,    decomposition 

\v,  20 

Hygroscopic  capacity  of  soils.  1!)4 
coeflicient  from  other  constants, 

formula-,    1!)7 
of  soils,    10(i 
relation  to  wilting  coefficient, 

107 
moisture,    affected    by    colloids, 

195 

by  humidity,  190 
by  organic  matter,   190 
by  si/e  of  particles,  194 
by  temperature,  195 
chapter  on,   194 
use  of,    107 

Ice-laid  deposits,  chapter  on.  41 
Igneous   rocks,    ti 
Ignition,  loss  on,   154 
Implements    of    tillage,    compactors, 
335 


Implements    of    tillage,    cultivators, 

337 

harrows,    332 
listers,   332 
plows,  327 
seeders,  337 
Insects,   controlled  by  rotation,  377 

mix  soil,  315 

Interglacial   stages,  Aftonian,  40 
1'eorian,  48 
Sangamon,  47 
Yarmouth,  40 

Internal   area  or  surface,    181 
Intrusive  rocks,  0 
lowan  glaciation,  48 

important    loess   deposit   con- 
nected with,  02 

Irrigated  land,  crops  for,  alfalfa,  275 
cereals,  273 
forage   crops,  275 
fruits,    275 
sugar   beets,   275 
vegetables,  275 
Irrigation,    chapter   on,   257 

bv    overhead    sprav    or    sprink- 

"  ling.  272 

canals   lined  with   concrete,  25,'; 
cultivation    after,    27-'! 
efl'ect  of,   on    rise   of   alkali,    2>Sl 
in  humid  climates.  275 
methods  of,   Hooding,  270 
furrow,   271 
sprinkling  or  overhead  spravs, 

272 

sub-irrigation,  272 
potatoes   by   furrows.  271 
preparation  of  land  for.  250 
projects  in  I'nited  States.  257 
in   varied   quantities,  yield  of 

dry  matter,  204 
sources       of,       diversion       of 

streams,  258 
pumping    from    streams    or 

canals.    250 
reservoirs.    259 
subterranean   supply.  250 
water,  character  of,  '201 
time  of.  •_'<;:! 

Illinois  soil    survey.    112 
Illinoisan  glacial  ion.  47 

•  lardinc.  \V.   M.,  yiejd  of  milo  mai/e. 

Texas.    25.'5 
Jersevan    or    Nehraskan    glaciation, 

40  ' 
Johnson.    S.    W.,    carbon    dioxide    in 

soil  air,  20 


430 


INDEX 


Kames,  formation  of,  45 
Kansan   glaciation,   46 
Karraker,     substances     in     solution 
play  little  part  in  capillary  move- 
ment, 205 

Keewatin  center  of  accumulation,  45 
King,  F.  H.,  amount  of  soil  carried, 
Mississippi  River,  35 

aspirator,    128 

computed  surfaces  of  soil  par- 
ticles of  different  kinds  of 
soil,  181 

depth  of  mulches,  235 

difference  in  temperature  due  to 
slope,  305 

effect  of  drainage  on  tempera- 
ture, 224 

effect  of  windbreak  on  evapora- 
tion, 301 

manure  in  surface  causes  rise 
of  water  into  upper  three  feet, 
212 

movement  of  moisture  from  wet 
to  dry  soil  slow,  203,  204 

rain  caused  rise  of  water  from 
subsoil,  205 

sampling  tube,  119 

spring  discharge  greater  with 
falling  barometer,  219 

water  evaporated  with  water 
table  at  varied  depths  below 
surface,  210 

water  used  per  pound  of  dry 
matter,  188 

weight  of  particles  with  film  of 
water,  33 

Labradorean     center     of     accumula- 
tion, 45 

Lacustrine  soils,  37 
Lake  Agassiz,  38 
beds,  37 
Chicago,  38 

level  floor  with  distinct  shore 

line,  37 

filling  with  peat,  method  of,  29 
Maumee,  38 

terraces  and  beaches,  37 
Lakes,  ox-bow,  28 
Lands,  alkali,  278 

value  of,  290 
preparation    of,    for    irrigation, 

259 

surface  lowered  through  solu- 
tion of  limestone,  24 


Lang,  specific  heat  of  soil  constit- 
uents, 299 
Lapham,  J.  E.  and  M.  H.,  Bureau  of 

Soils,  soil  survey,  78-111 
latitude,  affecting  organic  content 

of  soils,   145 
or  angle  of  sun's  rays  affecting 

soil  temperature,  304 
Lawes    and    Gilbert,    water    trans 
pired  by  growing  plants  per  pound 
of  dry  matter,  188 
Leaching  of  manure,   factor  in   loss 

of  organic  matter,  164 
of  soil,  organic  matter  lost  bv, 

152 

nitrates  lost  by,  322 
Legumes,   composition    of   tops   and 

roots,  398 

Level  bench  terrace,  366 
Leverett,    F.,    connects    loess    with 

lowan  glaciation,  62 
depth  of  drift,  Illinois,  42 
run-off  for  Illinois  river  basin, 

358 
Light,  effect  of,  upon  soil  bacteria, 

321 

•'  Light "  soil,  defined,  134 
Liquid   manure,    value   of,    excreted 

by  farm  animals,  162 
Lime,  403 

and  magnesia  in  soils,  75 
carbonate    carried    by   Thames 

River,   23 

effect    of,    on    number    of    bac- 
teria, 321 
on  flocculation,  137 
forms  of,  air-slaked  lime,  lime- 
stone, marl,  quicklime,  405 
in   prairie  compared   with   tim- 
ber soils,  75 
quick-,   loss   of   organic   matter 

due  to  use  of,   152 
Limestone,  403 

addition  of,  aid  in  producing  or- 
ganic matter,  158 
and  rock  phosphate,  effect  of,  on 

growth  of  clover.  159 
application  of,  aid  in  preventing 

erosion,   361 
best  form  to  apply,  406 
boulder  with   glacial   scratches, 

42 

calcite,  5 

composed  chiefly  of  shells,  9 
containing  crinoid  stems,  9 


INDEX 


431 


Limestone,     effect     of     carbonated 

water  on,  22 
factor    in    maintaining    organic 

content  of  soil,  145 
Valleys   and   Uplands  province, 

83 

Lister,  work  of,  331 
Lithological   factor  in  classification 

of  soils,  73 
lx>ams,  115 
clay,  115 
graVelly,    1 16 
peaty,  114 
sandy,  116 
fine,   116 
silt,  115 
stony,  116 
Locust,  black,  holds  sand,  59 

growing  on  gullied  land  pre- 
vents erosion,  308 
Loess   and   dust,   physical   analyses, 

64 

chemical  analyses  of,  65 
defined,  61 
deposit,   connected   with    lowan 

glaciation,  62 
deposits,  48 
formation  of,  62 
"kindchen,"  lime  concretions,  62' 
occurrence  of,  61 
origin  of,  61 
texture  uniform,  64 
ertieal  walls  or  cleavage,  char- 
acteristic of  deep,  63 
Loosening  soil,  an  object  of  tillage, 

325 
Loss    by   evaporation,    effect   of,   on 

transpiration,  191 
of  manure   and   its   prevention, 

163 
on    ignition,    154 

compared   with   organic   mat- 
ter. 154 

Losses  of  organic  matter,  151 
Ixnighridge,   rise  of  water   in   clay. 

206 

Lyon,  T.  L..  and  Fippin,  E.  O..  sur- 
face tension  and  density  of  certain 
solutions,  206 
Lynde  and  Diipre,  capillary  pull.  211 

osmosis  in  soils,  212 
Lysimeters  or  drain  gages,  220 

Macro-organisms,   insects,    315 
plants.  316 
rodents,  315 
worms,  315 


Magnesia  in  prairie  compared  with 

timber  soils,  75 
and  lime  in  soils,  75 
Magnesium  carbonate,  dolomite,  5 
Magnetite,  6 
Maintaining  and  increasing  organic 

matter  in  soils,  chapter  on,  158 
Major  crops,  defined,  376 
Mangrove  marsh,  Florida,  37 
Mangum  terrace,  366,  367 
Manure,  barnyard,  161 

conserved  by  use  of  absorbents, 

165 
farmyard,   influence  of,  on  soil 

temperature,  294 
nitrogen  content  of,  399 
fresh,  composition  of,  163 
green,  160 

loss  of,  and  its  prevention,  163 
by  fermentation,  164 
by   leaching,   164 
organic  matter,  in  rotting  of, 

163 
methods  of  applying,  168 

of  handling,  165 
solid   and   liquid,   value   of,  ex- 
creted by   farm  animals,   162 
spreader  in  action,  167 
steer,  composition  of,  after  ex- 
posure, 166 
value   of    increase   due   to,   per 

ton,   168 

Marbut,  C.  F.,  and  others,  area  re- 
sidual soils  in  United  States, 
mapped,  27 

Bureau  of  Soils,  soil  survey,  78 
Marine  soils,  36 
Marl,  8 

Marram,  or  beach  grass,  transplant- 
ing, 56 
Marsh,  marine,  section  of,   36 

mangrove,    Florida,    37 
Marshes,  early  stages  of  formation, 

map,  36 
defined.  27 
Martin.   F.   O..  and   others,   chromic 

acid  method,   154 

Material   in  solution  in  streams,  24 
Maumee.  Lake,  38 
Maximum  water  capacity  of  soils.  209 
MeLane,      with      Hriggs,      moisture 

equivalent   centrifuge.    202 
Meadows,  hold   soil   against   erosion, 

361 

Measurement    of     irrigation     water, 
268 


432 


INDEX 


Mechanical    analysis,    methods    of, 

124-128 

or  physical  analysis,   123 
Merrill,  (».  P.,  composition  of  feld- 
spars, 3 
expansion  of  granite  by  hydra- 

tion,  21 
glass     ground     by     wind-borne 

sand,    19 
table,      chemical      analyses     of 

loess,    05 
on    lo.ss    of    constituents    of 

rocks,  25 

physical  analysis  of  dust,  64 
Merrill,   L.   A.,   yield   of   wheat    for 
different  depths  of  plow- 
ing, 245 

methods  of  seeding,  254 
Metamorphic  rocks,   10 
Methods  of  soil  survey,  118 
Mica,  black,  biotite,  4 

white,  muscovite,  4 
Micro-organisms,  injurious,  317 

beneficial,    317 
Migratory  sand  dunes,  58 
Miller,    M.    F.,    plant    food   in   Mis- 
souri soils,  392 
Mineral  colloids,  132 

constituents    of    soils,    chapter 

on,  123 

content  of  soils,  74 
phosphorus-bearing,  apatite,  5 
soil  constituents  and  their  prop- 
erties, 129 
Minerals,    dissolved    by    carbonated 

water,  22 
hardness   of,   2 

iron-bearing,    hematite,    magne- 
tite,  limonite,  5,  6 
soil  forming,   1 

specific  gravity  of,  175 
Minor   crops,   376 

Mississippi  River,  soil  material  de- 
livered at  mouth,  35 
Moisture,  available,  214 

increased  by  drainage,  223 
capacity  of  soil,  methods  of  in- 
creasing, compacting 
soil,   230 

deep  rooting  crops,  231 
organic  matter,  231 
tillage,  230 
control  of,  chapter  on,  222 

by  tillage,  chapter  on.  230 
content,  ways  of  expressing,  191 


Moisture  content,  ways  of  express- 
ing, acre-inches,   192 
cubic  inches,  or  per  cent 

of  volume,  192 
per    cent    of    weiglut    of 

soil,    191 
decreasing,     losses     from    soils, 

232 

effect   of,   on   specific  heat,   300 
equivalent,   defined,    202 

determination  of,  from  other 

constants,  formulae  for,  203 

equivalents  of  some  soil  classes, 

202 

excess  of,  removed  by  tillage,  231 
factor    in    amount    of    organic 

matter  in  soils,  143 
soil  classification,  73 
for  bacteria,  319 
-holding  capacity  of   soils,   209 
hygroscopic,  chapter  on,  194 
in  soil   columns,  201 
retained  by  organic  matter,  149 
storing  and  conserving  by  till- 
age,  326 

supply  in  soils,  189 
Moraine,    terminal,    43 
Morrow,  G.  W.,  results  of  root  prun- 
ing in  shallow  and  deep  cultiva- 
tion of  corn,  355 
Moss,    sphagnum,   28 
Mucks,   114 

specific  heat  of,  300 
Mud  flow,  Colorado,  34 
Miiller,    Richard,    solution    of    min- 
erals, 22 

Mulch,  defined,  233 
depth   of,   235 
fineness  of,  234 
maintenance   of,   236 
soil    effectiveness    of,    235 
value    of,    for    corn,    humid    re- 
gions, 350 
Mulches,  permit  little  loss  of  water 

by    interstitial    evaporation,    233 
Muscovite,  white  mica,  4 

Xebraskan   glaciation,   or   .Terseyan, 

46 
Nelson,  J.  B.,  with  Atkinson,  storing 

rainfall,   Montana,   248 
Newell,    Dr.    F.    H.,    directed    large 

irrigation    projects,    258 
Nitrates  lost  from  soil  by  leaching, 

322 
by   denitrification,   323 


INDEX 


433 


Nitrate  production,  effect  of  potas- 
sium carbonate  upon,  321 
Nitric    acid,     amount     brought     to 

earth,  Rothamsted,  20 
decomposition  by,  20 
Nitrification,  .317' 

increased  by  drainage,  225 
loss  of  organic  matter  by,  152 
temperature  for,  21)8 
Nitrogen,    393 

commercial  forma  of,  ammonium 

sulphate,  399 
calcium    cyanamid,   400 
organic  substances,  400 
sodium  nitrate,  399 
content   of  humus,    147 
fixation,  317 
furnished    to   crops   by   organic 

matter,   151 

in  fertilizing  materials,  405 
in  humus   from  different  mate- 
rials,  147 

lost  by  erosion,  3f>0 
Non-tilled    crops,    factor    in    main- 
taining organic  matter.   171 
Northwestern       International       Re- 
gion, 105 
Number  of  particles,   178 

Oats  production,  1909,  414 

seed  bed  for,  349 
Objects  of  a  soil  survey,   117 
Oblique    arrangement    of    particles, 

180 

Odor  of  soils,  177 

Optimum  water  content,  defined,  212 
Organic  colloids,  132 

constituents    of    soils,    chapter 

on,  142 
matter,    addition    of,    as    sweet 

clover,  172 
affecting  capillarv  movement, 

200-208 

hygroscopic    moisture,    190 
and     fertility,     loss     of,     in 

rotting  of   manure,    103 
and  nitrogen,  lost  by  erosion. 

3fiO 

changes   of,    145 
comparison,  chromic  acid  and 

combustion  methods,   155 
defined.  142 
distribution  of,  in  soil  strata. 

147 
effect   of.  on   percolation,  218 

on  shrinkage,  130.  135 
in  sweet  clover,  173 
28 


Organic  matter  increased  by  plowing 

under  legumes,  172 
increases     moisture  -  holding 

capacity,  231 
increasing  amount  of,  aid  in 

checking  erosion,  303 
in   soils,   amount  of,   depends 
on   altitude,    145 
on  latitude,   145 
on  limestone,  145 
on  moisture,  143 
on  vegetation,  144 
kinds     of,     active,     coal-like, 

inert,   142 
loss     on     ignition     compared 

with,  154 

losses  of,  by  cropping,  151 
by  erosion.  151 
by  fallowing,  153 
by  fires,  152 
by  leaching,  152 
by  quicklime,   152 
methods  of  estimation  of.  153 
chromic  acid  method.  154 
combustion      in      oxygen, 

154 

loss  on   ignition.   154 
maintaining,  accumulations 

in  pastures,   100 
barnyard  manures,   1(51 
catch    and    cover    crops, 

161 

green  manures.  100 
limestone,      addition      of, 

158 
non-tilled  crops,  growing 

of,    171 
organic    residues,   use   of, 

170 
phosphorus,     application 

of.    15!) 

rotation  of  crops.  171 
of  soils,  maintaining  and    in- 
creasing, chapter  on.  158 
turning    under    and    incorpo- 
rating with    soil,   object    of 
tillage.  325 
residues.    170 

substances     lower     surface    ten- 
sion. 205 

source  of  nitrogen.  400 
Organisms,  soil,  chapter  on,  31.1 
beneficial.  317 

injurious,  as  plant  diseases,  317 
Origin   of  alkali.   278 
of  soil  material,  1 


434 


INDEX 


Osborne,  grades  of  particles,  124 
Osmosis,  temperature  for,  298 
Osmotic    pressure,    sugar    solution, 

131 

Ox-bow  lakes,  28 
Oxidation,  20 

expansion  caused  by,  21 
loss  of  organic  matter  by,  152 
Oxygen,    combustion    in,    determina- 
tion of  organic  matter,  154 

Packing,  subsurface  in  dry  farming, 

247 

Pacific  Coast  Region,  107 
Particles,  colloid,  size  of,  130 

soil,  and   their   separation,    123 
arrangement  of,  179 
number  of,  178 
shape  of,  178 
size  of,  affecting  hygroscopic 

moisture,   194 

Pastures,  accumulations  in,  aid  in 
maintaining  organic-matter 
content,  160 

hold  soil  against  erosion,  361 
Patten,  H.  E.,  specific  heat  of  soils, 

300 
effect    of    moisture    on    specific 

heat,  300 
Pearce,  J.  R.,  size  of  particles,  124 

chromic  acid  method,  154 
Peat,  filling  lake,  29 

method  of  formation,  28 
Peats,  114 
Peaty  loams,  114 
Peorian   interglacial   stage,   48 
Percolation,  affected  by  atmospheric 

pressure,  219 
by  granulation,  218 
by  organic  matter,  218 
by  physical  composition  of  soil, 

217 

by   roots   of   plants,   219 
by  shrinkage  cracks,  219 
by  viscosity  of  water,  219 
defined,  217 
evaporation,    rainfall,    Rotham- 

sted,  220 
large   and    small,   effect   of,   on 

yield  of  wheat,  153 
loss  of,  by  water,  in  dry  farming, 

242 

source  of  loss  of  water,  232 
Pfeffer,     osmotic     pressure,     sugar 
solution,  131 


Phosphate,  rock,  and  limestone,  ef- 
fect on  growth  of  clo- 
ver, 159 
on  wheat,  401 

Phosphorus,   application    of,   aid    in 
producing  organic  matter,  159 
forms  of,  acid  phosphate,  402 
basic   slag,   402 
bone  meal,  400 
compared,  402 
rock    phosphate,    400 
in  fertilizing  materials,  405 
Physical  agencies  of  weathering,  12 
analyses  of  loess  and  dust,  64 
analysis,   methods    of,    124 
aspirator.  King's,  128 
centrifugal,     Bureau    of 

Soils,  127 

elutriator,    Yoder's,    128 
churn  elutriator,  Hilgard's, 

126 

elutriator,   Schone,    124 
sieve,   124 
subsidence,  124 
systems    of,    124 
changes,  source   of  soil  heat,  294 
character  of  soil  changed  by  ero- 
sion, 360 
of  water,   186 
composition   of  soil   in   relation 

to  bacteria,  321 
affecting   percolation,    217 
of  soils,  varied,  effect  of,  on 

porosity,  184 

condition    of   soil,   effect   of   al- 
kali on,  280 

or  mechanical  analysis,   123 
properties  of  soils,  chapter  on, 

175 
apparent    specific    gravity, 

175 
arrangement    of    particles, 

179 

color,  176 
internal    area    or    surface, 

181 

odor,   177. 

number  of  particles,   178 
porosity,    182 
real  specific  gravity,  175 
shape  of  particles,  178 
weight,   1 76 

Pines  growing  on  sand,  60 
Placing    of    soil    material,    chapter 
on,  27  . 


INDEX 


435 


Plant   diseases    controlled    by    rota- 
tion, 377 

food,  crop  requirements,  390 
elements  of,  390 
in   crops,  3!)0 

in   Illinois  soils,  surface,  394 
subsoil,  390 
subsurface,  395 
in  Missouri  soils,  392 
in  residual  soils,  392 
in  Russian  soils,  392 
locked  up  in  mulches,  230 
supply  in  soils,  391 
Planting  seed  accompanied  by  some 

tillage,    326 
Plants,    amount    of    water    required 

by,  187 

disintegration   by,   19 
effect  of  alkali  on,  282 

on  rocks.  24 
remains  benefit  soil,  310 
water  requirements,  241 
Plasticity   of   clays,    135 
Plow,  an  early  form  of,  340 
pan  or  sole.  70 
theoretical   action   of.   327 
Plowing.   340 

deep,  and  turning  under  alkali. 

280 

contour,  aid  in  checking  ero- 
sion,  304 
tilling.  345 
depth  of.  344 
fall,   desirable   in   dry   farming. 

246 

good,  essentials  of,  341 
sod  well  turned,  341 
poor,  crooked  furrow,  342 
subsoiling,    345 
time  of,  342 
fall,  343 
spring,  344 

yields    of    wheat    for    different 
depths  of.  in  dry  farming,  245 
Plows,  deep  tilling  double  disk,  331 
disk.  329 

general  purpose,  328 
lister.  332 
sod.    329 
stubble.  328 
subsoil,   332 
Plutonic  rocks,  0 

Pore  space,  amount  of  in   soils.    ISO 
Porosity,    different    grades    of    sand, 

183 
of  soils,    182 


Porosity  of  soils,  of  varied  physical 

composition,  184 
Potassium,   403 

effect    of,    on    corn    on    swamp 

land,  404 

in  fertili/.ing  materials,  405 
Potatoes,  on  dry  farm,  253 
Pott,    11.    E.,    relative    conductivity 

of  soil    material,   300 
Prairie  areas  of   United   States,   70 

soils,   70 

Precipitates,  chemical,  8 
Precipitation,  map  of  United  States, 

190 

on  earth's  surface,  189 
source  of  soil  heat,  294 
Preparation  of  seed  l>ed,  345 
Press  drill,  337 
Pressure,    atmospheric,    changes    in, 

factor  in  ai:ration,  311 
of  waves.  18 
Prestwich,    lime    carbonate    carried 

by  Thames  River.  23 
Prevention   of  loss  of  manure.    103 
Properties,    physical,   of  soils,  chap- 
ter on,   17.") 
Puddling  of  clays,    136 

prevented  by  organic  matter.  150 
Pulverixing    and    loosening    soil,    an 

object   of  tillage,   325 
Pumping   water    for    irrigation,   259 
Pyroxene.    3 

Quaking  bog.   28 
Quart/,   2 

Radiation,  factor  in  loss  of  soil  heat, 

295 

from  sun.  source  of  soil  heat,  293 
of   heat,  effect  of,   on   soil    tem 

peraturc.   302 

ratio,  different  colored  soils,  295 
Rainfall,  affecting  transpiration.  18!) 
and  evaporation  from  free-water 
surface.    241 

Rothnmsted.    211 
and      snow.      precipitation      on 

earth's    surface.    189 
character   of.   effect    on    erosion. 

359 
factor    in    value    of    region    for 

dry    farming,    238 
map  of  United  States.  190 
percolation,    evaporation.    Roth- 

amsted,   220 


436 


INDEX 


Rainfall,  storing  of,  in  dry  farming, 

247 
types  of,  over  dry-land  area  of 

United  States,   239 
Reaction,  alkaline,  of  soil  desirable 

for  bacteria,  320 

Reade,  rate  of  lowering  of  land  sur- 
face by  solution,  24 
Real  or  absolute  specific  gravity,  175 
Reclamation   of   alkali    lands,   chap- 
ter on,  278 
Redding,  R.  J.,  depth  of  plowing  for 

cotton  on  eroded  land,  364 
Reforesting  stops  erosion,  369 
Reservoirs,  storing  water  for  irriga- 
tion, 259 
Residual  soils,  27 
Residues,  organic,  17D 

return  of,  aid  in  preventing  ero- 
sion, 363 

Resurrected  forest,  55 
Rhyolite,    7' 
River  Flood  Plains  province,  97 

sediments,    composition   of,   262 
swamps,  28 

water,  suspended  matter  in,  262 
Rock  disintegration  and  talus  slope, 

32 

outcrop,    116 
phosphate,   400 
split  by  tree,   19 
weathering  of  jointed,  31 
Rocks,  6 

aqueous,  7 

decomposition    and    disintegra- 
tion  of,   1 1 
eruptive,  6 

expansion  of,  on  heating,  13 
igneous,  6 
intrusive,    6 

loss  of  constituents  through  de- 
composition, 22 
metamorphic,  10 
plutonic,   6 
volcanic,  6 

weathering  of,  chapter  on,  11 
Rocky   Mountain    and    Plateau    Re- 
gion,  104 
Rodents,    mix    surface    and    subsoil, 

315 
Rogers  Brothers,  dissolved  minerals 

in  carbonated  water,  22 
Rollers,  335  to  337 
Roosevelt  dam,  260 
Root    injury,   353 

pruning  of  corn,  results,  355 


Root  systems,  depth  of,  varied  in  ro- 
tations, 378 

Roots    and    tops,    legumes,    compo- 
sition of,  398 
force    exerted    by,    19 
in  Chernozem  soils,   144 
of  plants  aid  percolation,   220 

tree  prying  rock  apart,  19 
Rotation,  chapter  on,  376 

advantages   of,   better   distribu- 
tion of  work,   377 
control   of   insects   and   plant 

diseases,   377 
of  weeds,  377 
compared  with  continuous  corn, 

Iowa,  379 
effect  of,  on  crop  yields,  Illinois, 

Ohio,  Minnesota,  379,  380 
for  corn  and  winter  wheat  belt, 

382 

cotton   belt,    384 
spring    wheat    belt,    386 
helps  maintain  good  tilth,  378 

organic  matter,  378 
produces  larger  yields,  378 
renders  toxic  substances  less 

harmful,    378 
variation    in    depth    of    root 

systems,  378 

of  crops,  aid  in  maintaining  or- 
ganic matter,  171 
place  for  crops  in,  381 
planning  of,  380 
Rotmistrov,  weeds  enemy  of  culture, 

friends  of  drought,  244 
water   not  raised   far  by  capil- 
larity at  Odessa,  210 
Run-off,  cause  of  loss  in  dry  farm- 
ing,  242 
Russell,  origin  of  adobe,  65 

Sage  brush  on  land  well  adapted  to 

dry  farming,  239 
Salts,  soluble,  in  soils,  74 
Sampling  of   soils,    120 
tube,    King's,    119 
Sand  dune,  bun-ing  forest,  55 

wind  ripples  on,  56 
dunes,  migratory  or  wandering, 

54,  58 

permanent  or  fixed,  54,  55 
held  by,  black  locusts,  59 
bunch  grass.  60 
partridge   pea,    59 
pines,  60 
sensitive  plant,  59 


INDEX 


437 


Sand  dunes,  held  by   trailing  wild 

bean, 60 
vegetation,  57 

movement  checked  by  fences,  58 
porosity  of  different  grades,  183 
Sands,   110 

and   sandv    loams,    properties 

of,  139  * 
radiation    ratio    of    different 

colors  of,  295 
temperature  of,  effect  of  color 

on,  302 
Sandstones,  8 
Sandy  loams,   116 
Sangamon   interglacial  stage,  47 

soil,  40 
Schlpsing,  relation,  nitrates  formed 

to  oxygen,  320 
Schone's  elutriator  method,  physical 

analysis,  124 
Schreiner,    O.,-  and    Brown,    E.    K., 

progress  of  hurnification,   14(5 
Sedentary   formations,   27 
Sediment  carried    in  suspension   by 

rivers,  35 

Seditnental  soils,  33 
classes  of.  36 

Sedimentary,  fragmental,  8 
Seed,   acclimated,    necessary    in    dry 

fanning,  255 
bed,    preparation    of,    for    corn, 

348 

for  oats,  349 
for  wheat,   346 
Seeders,  337 
Seeding,  different  methods  of,  yield 

wheat  on  dry  land,  254 
on  dry  land.  254 
rate  per  acre,  Colorado,  255 
Shaler,     wave     action,     Capo     Ann. 

Massachusetts,  18 
Shales,    8 

Shantz,  H.  L.,  see  Briggs 
Shape  of  particles,   178 
Shrinkage,  affected  by   colloids,   1  32 
cracks,   1 36 

effect  of.   on    percolation.   21!> 
physical      composition      of, 

135 
of  soils,   135 

different,  types  of  soil,   133 
Sieve  method,  physical  analysis,  124 
Silica,  2 
Silt   and    silt    loams,    properties    of, 

138 
dunes,  53 


Silt  loams,  115 
Sink  holes,  22 

in  cave  region,  24 

ponds,   produced   when  outlet 

is  clogged,  24 
Size   of  soil   particles,  effect  of,  on 

capillarity,  201 

Slope  of  land,  effect  of,  on  soil  tem- 
peratures, 305 
Snyder,    loss    of   organic    matter    in 

forest  fires,  152 
nitrogen  in  humus  from  vari- 
ous materials,   147 
Sodium  nitrate,  399 
Soil — soils 

air    and    aeration,    chapter    on, 

309 

carlxm  dioxide  in,  20 
composition  of,  310 
alluvial,  38 
amount  of  air  in,  309 

of  organic  matter  in,  142 
and  subsoil,  chapter  on,  67 
are  they   inexhaustible?  289 
arid,   74 
auger,  119 

Bureau   of,   classification,  chap- 
ter on,  78 
earried  in  suspension  hv  rivers, 

35 
capillary     or     moisture-holding 

capacitv  of,  209 
pull  of,  211 

character  of,  factor  in  its  adapt- 
ability to  dry  farming,  241 
Chernozem,  roots  and  humus  in, 

144 

class,  defined,  "!> 
classes  in  Illinois,  112 
clay  loams,  1 1  ."> 
clays,  114 
gravels.   11(5 
gravelly  loams.   116 
loams.   1 1  .'> 
mucks.    114 
peats,   11(5 
peaty  loams.  116 
sands,    1 1  6 
sandy   loams,   116 

fine,   11(5 
silt  loams,   115 

classification  of.  chapter  on.  72 
colloids   in.    132 
colluvial.   30 
color  of.    17(5 

effect  on  time  of  germination. 
304 


438 


INDEX 


Soils,  compacted  by  tillage,  326 

conductivity   of,   effect  on  tem- 
perature, 305 
constituents,    capillary    lift    of, 

212 

specific  heat  of,  299 
cumulose,  27 

deep,       medium -grained,       well 
adapted  to  dry  farming,  243 
definition  of,  1 

effect  of  alkali  on  physical  con- 
dition of,  280 
of  color  of,  on  growth,  303 
on  transpiration,  191 
eolial,  53 

erosion,  chapter  on,  358 
fertility,  appendix  I,  389 
-forming  minerals,  1 
glacial,  41 
gravelly,    not    well    adapted    to 

dry  farming,  240 
gravity-laid,  30 
gullies  filled  with,  374 
heat,     loss     of,     by    conduction 
downward  into  soil,   29(5 
by    convection    currents    of 

air,  296 
by    evaporation    of    water, 

296 

by  radiation,  295 
sources  of,  293 

chemical  changes,  294 
physical  changes,  294 
precipitation,  294 
radiation,  direct  from  sun, 

293 

"heavy,"   "light,"   defined,   134 
humid,  75 
hygroscopic  capacity  of,  194 

coefficient  of,  196 
Illinois,  fertility  in,  394 
Kentucky,  393 
lacustrine,   37 
lime  and  magnesia  in,  75 
marine  deposits,  36 
material  and  its  origin,  chapter 

on,    1 

placing  of,  27 

relative   conductivity   of,   306 
methods  of  increasing  moisture 

capacity  of,  230 

mineral    constituents    of,    chap- 
ter on,  123 
content  of,   74 
Missouri,  392 
mulch,  defined,  233 
mulches,   effectiveness   of,    235 


Soils,  odor  of,  177 

organic    constituents    of,    chap- 
ter on,   142 

organisms,   chapter   on,   315 
particles   and   their   separation, 

123 

held  together  by  organic  mat- 
ter, 151 
surfaces  of,  in  different  soils, 

181 
physical   character   of,   changed 

by  erosion,   360 
properties  of,  chapter  on,  175 
plant  food,  supply  in,  391 
porosity  of,  182-184 
prairie, .  75 
provinces,     area     surveyed     to 

1915,  78 
regions,  area  surveyed  to  1915, 

78 
residual,    27 

plant  food  in,  392 
running  together  hinders  aera- 
tion,   313 
samplers,    1 19 
sampling  of,    120 
Sangamon,  49 
sedimental,  33 

classes    of,    36 

series,  Bureau  of  Soils,  79-111 
shrinkage   of,    133,    135 
soluble  salts  in,  74 
specific  heat  of,  300 
strata,    distribution   of   organic 

matter  in,   147 
thickness  of.  120 
weight  of,  120 
stream-laid,  38 
subsurface,   67 
surface,  67 

survey  by  .bureau  of  Soils,  chap- 
ter on,   78 
by    Illinois    Experiment    S'ta- 

tion,  chapter  on,   1 12 
methods  of,  118 
objects  of,   117 
surveys,  116 

temperature,  chapter  on,  293 
conditions  affecting,   298 
absorption    and    radiation, 

302 

color,  303 
conductivity,  306 
drainage,  301 
evaporation,  300 


INDEX 


439 


Soils,    temperature,    conditions    af- 
fecting, latitude  or  angle 
of  sun's  rays,  .304 
slope,   304 
specific  heat,  298 
tillage,    307 

water,    presence    of,    302 
for  growth,  298 
for  vital  functions  of  plants, 

germination,   29(5 
growth,  297,  298 
nitrification,   298 
osmosis   and   diffusion, 

298 
influenced  by  liquid  water,  295 

by  manure,  294 
raised  by  absorption  of  water 

vapor,  294 

ten -year  average,  307 
texture  and  structure  of,  effect 

on  erosion,  358 
timber,   70 

time  for  heat  to  penetrate,  300 
top,  07 

type,  defined,  79 
types,  classes  and  phases  in  Illi- 
nois, 1 14 

defined,  Illinois,   112 
internal   area    of,    182 
naming  of,   113 
ventilation,  sec  aeration,  311 
water  of,   180-222 
water-laid,  33 
water-logged,   313 
weight   of,    170 
Sole,  plow,  70 
Solid  manure,  value  of,  excreted  by 

farm  animals,   102 
Solution,  decomposition  by,  22 
Specific  heat  of  water,   187 
gravity,  apparent.  175 

of  soil-form  ing  minerals,  17") 
real    or   absolute.    175 
Sphagnum  moss,  27,  28 
Spring  plowing,   344 

wheat,  acreage,    1909,   415 
region,  rotation  for,  380 
Stability  of  soil  increased  by  drain- 
age,  222 

Stalactites, stalagmites,  in  cavern. 23 
Stones,  139 
Stony  loams,  1 10 
Storm,  dust,  54 
Straw,  used  in   tilling  gullies,  370 


Streams,    diversion    of,     for    irriga- 
tion, 258 
erosion  of,  10 
-laid  soils,  38 
material  carried  and  rolled  bv, 

10 
work    of,    affected    by    velocity 

of  current.    10 

Strisc,  glacial,  on  rock  surface,  43 
Structure  of  soil,  effect  on  erosion, 

358 

Sub-provinces,    classes,    types,    sur- 
veys, chapter  on,  112 
Subsidence  method,   physical  analv- 

sis,   124 
Subsoil,  08 
plow,    330 

soil    and,    chapter    on,    07 
Subsoiling,  345 
Subsoils,  arid  and  humid  compared, 

70 

Substances  in  solution,  effect  on  vis- 
cosity,  205 
Subsurface  packing,  247 

soil,   07 
Sugar    beets,    returns     from     thirty 

inches  of  water,  200 
Sulfuric  acid,  decomposition   bv,   20 
Surface,  internal,  181 
soil,  07 
tension,     affecting     capillaritv. 

199 

and  density  of  solutions.  -JOO 
Survey,    soil,    by    Bureau    of    Soils, 

chapter  on,  78 
by    Illinois    Experiment    Sta- 
tion, chapter  on,  112 
methods  of,   118 
objects  of,   1 1  7 
Surveys,   soil.    110 

in   different   states,    117 
Swamp,  ablation,  30 

land,  typical   Eastern,  29 
wet  woods.  30 
Swamps,  defined,  27 

river,  28 
Sweet  clover  on   badlv   eroded   land, 

301 

plowed   under.    172 
quantity  grown  per  acre,   17.'! 
Syenite.   7 
Systems  of  physical  analysis,    124 

Talus.  30 

slope.  32 
Temperature,  chapter  on,  293 


INDEX 


Temperature,    affecting   hygroscopic 

moisture,  195 
viscosity,  204 

changes,  factor  in  aeration,  312 
climate,  factor  in  soil  classifica- 
tion, 73 
effect   of,   on   capillary   rise   of 

water,  204 

for  bacterial  development,  320 
germination,  296 

table  of,  297 
growth,  297 
nitrification,  298 
osmosis  and  diffusion.  29S 
of  plowed  and   unplowed   land, 

312 

sands,  effect  of  color  on,  302 
soil,  conditions  affecting,  298 

influenced  by  manure,  294 
raised  by  drainage,  224 

by  organic  matter,  150 
soil,  ten-year  average,  307 
time  required  for  radicle  to  ap- 
pear at  different,  297 
Tenacity  of  soils,  134 
Terminal  moraine,  formation  of,  45 

topography  of,  134 
Terrace,  glacial  lake  and  river  prov- 
ince, 89 

near  Rockford,  Illinois,  38 
Terraced  park,  Mississippi,  367 
Terraces  in  China,  364 

kinds  of,  guide-row,  365 
level  beach,  366 
Mangum,  366,  367 
method  of  formation,  39 
of  Frazier  River,  38 
Texture   of   soil,   affecting  capillary 

movement,  206 
percolation,  217 
effect  of,  on  erosion,  358 
factor  in  soil  classification,  77 
in  relation  to  bacteria,  321 
Thawing  and  freezing,  14 
Thickness  of  film  affecting  capillary 

movement,  203 

Thorne,  C.  E.,  composition  of  steer 
manure  after  three  months'  ex- 
posure, 166 

Thysell,  .1.  C.,  summer  tillage  with 
alternate  cropping  vs.  continuous 
cropping,  250 
Tight  clay,  68 

Tile   drainage,   effect   of,   on    topog- 
raphy of  water  table,  228 
Tile  drains.  228 


Tiling,  aid  in  checking  erosion,  369 
Tillage,  chapter  on,  325 

control  of  moisture  by,  230 
deep,  in  dry  farming,  245 
effect  of,   on  soil   temperature, 

307 

factor  in  aeration,  313 
increases   moisture   capacity,   230 
objects  of,  compacting  soil,  326 
killing  weeds,  326 
planting  seed,  326 
pulverizing      and      loosening 

soil,  325 

storing  and  conserving  moist- 
ure, 326 

turning  under  vegetable  mat- 
ter, 325 
removal   of   excess   of  moisture 

by,  231 

summer,  in  dry  farming,  246 
with  alternate  cropping,  com- 
pared       with        continuous 
cropping  yields,  250 
Tilling,  deep,  345 
Tilth,  rotation  helps  maintain,  378 
Timber  areas   of  United  States,   76 

soils,  76 
Time    for    germination    affected    by 

color  of   soil,   304 
at  different  temperatures,  297 
Top   soil,   67 

Topography,  effect  of,  on  erosion,  358 
Toxic    substances    less    harmful    in 

rotations,  378 
Trachyte,  7 
Transpiration,      dependent      upon 

evaporation,  191 
soil,  191 

supply    of    moisture,    189 
from  plants,   large  loss   of  wa- 
ter, 232 
of  water  per  pound,  dry  matter 

produced,    188 
source  ot   loss   in   dry   farming, 

244 

Transported  formations,  30 
Tull,   Jethro,   "  tillage   is   manure,'' 

325 

Type,   soil,   defined,    79 
Illinois,   defined,    112 

Udden,  J.  A.,  estimate,  dust  carried 

in  air,  53 
Uloth,  plants  germinated  on  ice,  296 


INDEX 


441 


Value   of   increase   for   manure   per 

crop   and  ton,   168 
organic  matter  to  soils,   148 

binds    soil    particles    to- 
gether, 151 
biological  effects,  150 
erosion,    loss    by,    pre- 
vented, 150 

furnishes  nitrogen,  151 
granulation  affected,   148 
moisture  retained,   149 
puddling  prevented,  150 
temperature   raised,    150 
Van  Slyke,  L.  L.,  per  cent  of  liquid 

and   solid   excrement,    162 
composition    of    fresh    manure, 

163 

Vegetation,  aid  in  filling  gullies,  374 
factor  in  soil  classification,  75 
source  of  soil  organic  matter, 

144 

Vegetative   covering,   effect   on  ero- 
sion, 350 

Velocity  of  current,  effect  of,  on 
size  of  material  carried, 
33 

on  work  of  streams,   16 
Ventilation    of   .soils,    311 
Vertical  cleavage  or  wall,  character- 
istic of  deep  loess,  63 
Viscosity  of  water,  187 

affecting  capillary  movement, 

204 

effect  of,  on   percolation,  210 
Volcanic  dust,  6 
rocks,  6 

Wandering  sand  dunes,  54,  58 
Water,  amount  of,  to  apply  in  irri- 
gation,  363 

re< |tiircd  by  plants,  187 
at  different  heights  above  water 

table,  drained,  217 
available,  213,  214 
capacity  of  soils,  maximum,  200 
capillary    rise    of,    affected    by 

temperature,  204 
in  glass  tubes,  199 
use  of,  212 
comparison    Iwtween    computed 

and  observed  flow  of,   129 
draining  from  eight  feet  of  satu- 
rated sand.  221 
duty  of,  267,  268 


Water  evaporated  daily  per  square 

foot  of  soil,  210 
evaporation    of,    effect    on    soil 

temperature,   296,   300 
for  irrigation,  character  of,  261 
gravitational,  chapter  on,  217 
height  and    apidity  of  capillary 

rise  in  different  soils,  207 
in  soil   in  one-foot  strata   to  8 

feet  deep,  248 
irrigation  in   varied  quantities, 

yield  of  dry  matter,  264 
-laid  soils,  33 

liquid,    effect   on    soil   tempera- 
ture, 205 
-logged   soil   prevents   aeration, 

313 

loss  of,  by  interstitial  evapora- 
tion, slight,  233 
from  canals,  266 
in  dry   farming  by   evapora- 
tion,  243 

by  percolation,  242 
by  run-off,  242 
by  transpiration,  244 
methods  of  preventing,  244 
deep  tillage,  245 
fall   plowing,   246 
storing   rainfall,   247 
subsurface    packing,    247 
summer  tillage,  246 
material  carried  by,  33 
measurement    and    distribution 

of,  in  irrigation,  268 
moved    by    capillarity,    amount 

of,  210* 
of  soils,  chapter  on,  186 

capillary,  chapter  on,   199 
physical  characteristics,  186 
presence  of,  effect  on  soil   tem- 
perature, 302 
producing    power   of,   in   varied 

application.  265 
removal  of  excess  of,  222 
factor  in  aeration.  311 
required  for  corn,  Utah.  242 
to    produce    one    pound    dry  i 

matter,  242 

requirement  of  plants,  241 
river,  suspended  matter  in.  2f>2 
table,    topography    of,    in    tiled 

land,  228 
transpired,  for  one  part  of  dry 

matter  produced,  188 
uses  of,  enumerated,   187 


442 


INDEX 


Water   vapor,   increase   in   tempera- 
ture by  absorption  of,  294 
viscosity  of,    187 
Waves,   disintegration  by,   pressure 

of,  18 

Weathering,  advanced,  12 
chemical  agencies  of,  19 
of  rock,  irregular  due  to  joints 

and  stratification,  1 1 
jointed,  31 

of  rocks,  chapter  on,  11 
physical  agencies,  12 
Weeder,  340 
Weeds,  controlled  bv  rotation,  378 

killing  of,  object  of  tillage,  326 
Weight  of  soil,  176 

strata,  120 
Wheat    belt,    winter,   rotations    for, 

382 

effect  of  rock  phosphate  on,  401 
methods  of  preparing  land  for, 

347 

Minidoka  project,  Idaho,  261 
production,  United  States,  1900, 

417 

seed  bed  for,  346 
yield,  different  methods  of  seed- 
ing,  254 
of  under   varied  percolation, 

153 

ten-year  average,  409 
without   irrigation,  Montana, 

249 
yields    for    different    depths    of 

plowing,  245 

Widtsoe,  J.  A.,  drv  matter  per  acre 
from  varied  amounts  of  irri- 
gation water,  264 
precipitation  on  earth's  surface, 
189 


Water,  producing  power  of  30  acre- 
inches    of    water    applied    to 
varied  areas,  265,  266 
rainfall    and   evaporation   from 

free- water  surface,  241 
suspended      matter      in      river 

waters,  262 
water  in  one-foot  strata  to  eight 

feet,  248 

Weir,  rectangular,  for  measuring  ir- 
rigation water,  268 
trapezoidal  or  Cippoletti,  269 
Wild  bean,  trailing,  holds  sand,  60 
Wiley,  H.  W.,  odor  of  soils,  177 
Wilting  coefficient,  defined,  212 

from     other     constants,     for- 
mulae, 213 
of  soils   for  different   plants, 

213 

relation    of    hygroscopic    co- 
efficient to,   197 
Wind-carved  granite,  18 
disintegration  by,   18 
movement,    factor    in    aeration, 

313 

ripples  on  sand,  56 
Winter  wheat  acreage,  1909,  416 
Wisconsin  glaciations,  50 
Wollny,    difference    in    temperature 

due  to  slope,  304 
water  transpired  per  pound  of 

dry  matter,   188 
Woods,  swamp,  wet,  30 
Work,  better  distributed  by  rotation, 
377 

Yarmouth  interglacial  stage,  46 
Yields  increased  by  rotations,  378 
Yoder,  P.  A.,  centrifugal  elutriator, 
128 

Zeolites,  4 


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